nanoflann.hpp

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/***********************************************************************
 * Software License Agreement (BSD License)
 *
 * Copyright 2008-2009  Marius Muja (mariusm@cs.ubc.ca). All rights reserved.
 * Copyright 2008-2009  David G. Lowe (lowe@cs.ubc.ca). All rights reserved.
 * Copyright 2011-2022  Jose Luis Blanco (joseluisblancoc@gmail.com).
 *   All rights reserved.
 *
 * THE BSD LICENSE
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *************************************************************************/
 
#pragma once
 
#include <algorithm>
#include <array>
#include <cassert>
#include <cmath>      // for abs()
#include <cstdlib>    // for abs()
#include <functional> // std::reference_wrapper
#include <istream>
#include <limits> // std::numeric_limits
#include <ostream>
#include <stdexcept>
#include <unordered_set>
#include <vector>
 
#define NANOFLANN_VERSION 0x150
 
// Avoid conflicting declaration of min/max macros in Windows headers
#if !defined(NOMINMAX) && (defined(_WIN32) || defined(_WIN32_) || defined(WIN32) || defined(_WIN64))
#define NOMINMAX
#ifdef max
#undef max
#undef min
#endif
#endif
// Avoid conflicts with X11 headers
#ifdef None
#undef None
#endif
 
namespace nanoflann
{
template <typename T> T pi_const() { return static_cast<T>(3.14159265358979323846); }
 
template <typename T, typename = int> struct has_resize : std::false_type
{
};
 
template <typename T> struct has_resize<T, decltype((void)std::declval<T>().resize(1), 0)> : std::true_type
{
};
 
template <typename T, typename = int> struct has_assign : std::false_type
{
};
 
template <typename T> struct has_assign<T, decltype((void)std::declval<T>().assign(1, 0), 0)> : std::true_type
{
};
 
template <typename Container>
inline typename std::enable_if<has_resize<Container>::value, void>::type resize(Container& c, const size_t nElements)
{
    c.resize(nElements);
}
 
template <typename Container>
inline typename std::enable_if<!has_resize<Container>::value, void>::type resize(Container& c, const size_t nElements)
{
    if (nElements != c.size())
        throw std::logic_error("Try to change the size of a std::array.");
}
 
template <typename Container, typename T>
inline typename std::enable_if<has_assign<Container>::value, void>::type assign(Container& c, const size_t nElements,
                                                                                const T& value)
{
    c.assign(nElements, value);
}
 
template <typename Container, typename T>
inline typename std::enable_if<!has_assign<Container>::value, void>::type assign(Container& c, const size_t nElements,
                                                                                 const T& value)
{
    for (size_t i = 0; i < nElements; i++)
        c[i] = value;
}
 
template <typename _DistanceType, typename _IndexType = size_t, typename _CountType = size_t> class KNNResultSet
{
  public:
    using DistanceType = _DistanceType;
    using IndexType = _IndexType;
    using CountType = _CountType;
 
  private:
    IndexType* indices;
    DistanceType* dists;
    CountType capacity;
    CountType count;
 
  public:
    explicit KNNResultSet(CountType capacity_) : indices(nullptr), dists(nullptr), capacity(capacity_), count(0) {}
 
    void init(IndexType* indices_, DistanceType* dists_)
    {
        indices = indices_;
        dists = dists_;
        count = 0;
        if (capacity)
            dists[capacity - 1] = (std::numeric_limits<DistanceType>::max)();
    }
 
    CountType size() const { return count; }
 
    bool full() const { return count == capacity; }
 
    bool addPoint(DistanceType dist, IndexType index)
    {
        CountType i;
        for (i = count; i > 0; --i)
        {
#ifdef NANOFLANN_FIRST_MATCH
            if ((dists[i - 1] > dist) || ((dist == dists[i - 1]) && (indices[i - 1] > index)))
            {
#else
            if (dists[i - 1] > dist)
            {
#endif
                if (i < capacity)
                {
                    dists[i] = dists[i - 1];
                    indices[i] = indices[i - 1];
                }
            }
            else
                break;
        }
        if (i < capacity)
        {
            dists[i] = dist;
            indices[i] = index;
        }
        if (count < capacity)
            count++;
 
        // tell caller that the search shall continue
        return true;
    }
 
    DistanceType worstDist() const { return dists[capacity - 1]; }
};
 
struct IndexDist_Sorter
{
    template <typename PairType> bool operator()(const PairType& p1, const PairType& p2) const
    {
        return p1.second < p2.second;
    }
};
 
template <typename IndexType = size_t, typename DistanceType = double> struct ResultItem
{
    ResultItem() = default;
    ResultItem(const IndexType index, const DistanceType distance) : first(index), second(distance) {}
 
    IndexType first;     
    DistanceType second; 
};
 
template <typename _DistanceType, typename _IndexType = size_t> class RadiusResultSet
{
  public:
    using DistanceType = _DistanceType;
    using IndexType = _IndexType;
 
  public:
    const DistanceType radius;
 
    std::vector<ResultItem<IndexType, DistanceType>>& m_indices_dists;
 
    explicit RadiusResultSet(DistanceType radius_, std::vector<ResultItem<IndexType, DistanceType>>& indices_dists)
        : radius(radius_), m_indices_dists(indices_dists)
    {
        init();
    }
 
    void init() { clear(); }
    void clear() { m_indices_dists.clear(); }
 
    size_t size() const { return m_indices_dists.size(); }
    size_t empty() const { return m_indices_dists.empty(); }
 
    bool full() const { return true; }
 
    bool addPoint(DistanceType dist, IndexType index)
    {
        if (dist < radius)
            m_indices_dists.emplace_back(index, dist);
        return true;
    }
 
    DistanceType worstDist() const { return radius; }
 
    ResultItem<IndexType, DistanceType> worst_item() const
    {
        if (m_indices_dists.empty())
            throw std::runtime_error("Cannot invoke RadiusResultSet::worst_item() on "
                                     "an empty list of results.");
        auto it = std::max_element(m_indices_dists.begin(), m_indices_dists.end(), IndexDist_Sorter());
        return *it;
    }
};
 
template <typename T> void save_value(std::ostream& stream, const T& value)
{
    stream.write(reinterpret_cast<const char*>(&value), sizeof(T));
}
 
template <typename T> void save_value(std::ostream& stream, const std::vector<T>& value)
{
    size_t size = value.size();
    stream.write(reinterpret_cast<const char*>(&size), sizeof(size_t));
    stream.write(reinterpret_cast<const char*>(value.data()), sizeof(T) * size);
}
 
template <typename T> void load_value(std::istream& stream, T& value)
{
    stream.read(reinterpret_cast<char*>(&value), sizeof(T));
}
 
template <typename T> void load_value(std::istream& stream, std::vector<T>& value)
{
    size_t size;
    stream.read(reinterpret_cast<char*>(&size), sizeof(size_t));
    value.resize(size);
    stream.read(reinterpret_cast<char*>(value.data()), sizeof(T) * size);
}
struct Metric
{
};
 
template <class T, class DataSource, typename _DistanceType = T, typename IndexType = uint32_t> struct L1_Adaptor
{
    using ElementType = T;
    using DistanceType = _DistanceType;
 
    const DataSource& data_source;
 
    L1_Adaptor(const DataSource& _data_source) : data_source(_data_source) {}
 
    DistanceType evalMetric(const T* a, const IndexType b_idx, size_t size, DistanceType worst_dist = -1) const
    {
        DistanceType result = DistanceType();
        const T* last = a + size;
        const T* lastgroup = last - 3;
        size_t d = 0;
 
        /* Process 4 items with each loop for efficiency. */
        while (a < lastgroup)
        {
            const DistanceType diff0 = std::abs(a[0] - data_source.kdtree_get_pt(b_idx, d++));
            const DistanceType diff1 = std::abs(a[1] - data_source.kdtree_get_pt(b_idx, d++));
            const DistanceType diff2 = std::abs(a[2] - data_source.kdtree_get_pt(b_idx, d++));
            const DistanceType diff3 = std::abs(a[3] - data_source.kdtree_get_pt(b_idx, d++));
            result += diff0 + diff1 + diff2 + diff3;
            a += 4;
            if ((worst_dist > 0) && (result > worst_dist))
            {
                return result;
            }
        }
        /* Process last 0-3 components.  Not needed for standard vector lengths.
         */
        while (a < last)
        {
            result += std::abs(*a++ - data_source.kdtree_get_pt(b_idx, d++));
        }
        return result;
    }
 
    template <typename U, typename V> DistanceType accum_dist(const U a, const V b, const size_t) const
    {
        return std::abs(a - b);
    }
};
 
template <class T, class DataSource, typename _DistanceType = T, typename IndexType = uint32_t> struct L2_Adaptor
{
    using ElementType = T;
    using DistanceType = _DistanceType;
 
    const DataSource& data_source;
 
    L2_Adaptor(const DataSource& _data_source) : data_source(_data_source) {}
 
    DistanceType evalMetric(const T* a, const IndexType b_idx, size_t size, DistanceType worst_dist = -1) const
    {
        DistanceType result = DistanceType();
        const T* last = a + size;
        const T* lastgroup = last - 3;
        size_t d = 0;
 
        /* Process 4 items with each loop for efficiency. */
        while (a < lastgroup)
        {
            const DistanceType diff0 = a[0] - data_source.kdtree_get_pt(b_idx, d++);
            const DistanceType diff1 = a[1] - data_source.kdtree_get_pt(b_idx, d++);
            const DistanceType diff2 = a[2] - data_source.kdtree_get_pt(b_idx, d++);
            const DistanceType diff3 = a[3] - data_source.kdtree_get_pt(b_idx, d++);
            result += diff0 * diff0 + diff1 * diff1 + diff2 * diff2 + diff3 * diff3;
            a += 4;
            if ((worst_dist > 0) && (result > worst_dist))
            {
                return result;
            }
        }
        /* Process last 0-3 components.  Not needed for standard vector lengths.
         */
        while (a < last)
        {
            const DistanceType diff0 = *a++ - data_source.kdtree_get_pt(b_idx, d++);
            result += diff0 * diff0;
        }
        return result;
    }
 
    template <typename U, typename V> DistanceType accum_dist(const U a, const V b, const size_t) const
    {
        return (a - b) * (a - b);
    }
};
 
template <class T, class DataSource, typename _DistanceType = T, typename IndexType = uint32_t> struct L2_Simple_Adaptor
{
    using ElementType = T;
    using DistanceType = _DistanceType;
 
    const DataSource& data_source;
 
    L2_Simple_Adaptor(const DataSource& _data_source) : data_source(_data_source) {}
 
    DistanceType evalMetric(const T* a, const IndexType b_idx, size_t size) const
    {
        DistanceType result = DistanceType();
        for (size_t i = 0; i < size; ++i)
        {
            const DistanceType diff = a[i] - data_source.kdtree_get_pt(b_idx, i);
            result += diff * diff;
        }
        return result;
    }
 
    template <typename U, typename V> DistanceType accum_dist(const U a, const V b, const size_t) const
    {
        return (a - b) * (a - b);
    }
};
 
template <class T, class DataSource, typename _DistanceType = T, typename IndexType = uint32_t> struct SO2_Adaptor
{
    using ElementType = T;
    using DistanceType = _DistanceType;
 
    const DataSource& data_source;
 
    SO2_Adaptor(const DataSource& _data_source) : data_source(_data_source) {}
 
    DistanceType evalMetric(const T* a, const IndexType b_idx, size_t size) const
    {
        return accum_dist(a[size - 1], data_source.kdtree_get_pt(b_idx, size - 1), size - 1);
    }
 
    template <typename U, typename V> DistanceType accum_dist(const U a, const V b, const size_t) const
    {
        DistanceType result = DistanceType();
        DistanceType PI = pi_const<DistanceType>();
        result = b - a;
        if (result > PI)
            result -= 2 * PI;
        else if (result < -PI)
            result += 2 * PI;
        return result;
    }
};
 
template <class T, class DataSource, typename _DistanceType = T, typename IndexType = uint32_t> struct SO3_Adaptor
{
    using ElementType = T;
    using DistanceType = _DistanceType;
 
    L2_Simple_Adaptor<T, DataSource, DistanceType, IndexType> distance_L2_Simple;
 
    SO3_Adaptor(const DataSource& _data_source) : distance_L2_Simple(_data_source) {}
 
    DistanceType evalMetric(const T* a, const IndexType b_idx, size_t size) const
    {
        return distance_L2_Simple.evalMetric(a, b_idx, size);
    }
 
    template <typename U, typename V> DistanceType accum_dist(const U a, const V b, const size_t idx) const
    {
        return distance_L2_Simple.accum_dist(a, b, idx);
    }
};
 
struct metric_L1 : public Metric
{
    template <class T, class DataSource, typename IndexType = uint32_t> struct traits
    {
        using distance_t = L1_Adaptor<T, DataSource, T, IndexType>;
    };
};
struct metric_L2 : public Metric
{
    template <class T, class DataSource, typename IndexType = uint32_t> struct traits
    {
        using distance_t = L2_Adaptor<T, DataSource, T, IndexType>;
    };
};
struct metric_L2_Simple : public Metric
{
    template <class T, class DataSource, typename IndexType = uint32_t> struct traits
    {
        using distance_t = L2_Simple_Adaptor<T, DataSource, T, IndexType>;
    };
};
struct metric_SO2 : public Metric
{
    template <class T, class DataSource, typename IndexType = uint32_t> struct traits
    {
        using distance_t = SO2_Adaptor<T, DataSource, T, IndexType>;
    };
};
struct metric_SO3 : public Metric
{
    template <class T, class DataSource, typename IndexType = uint32_t> struct traits
    {
        using distance_t = SO3_Adaptor<T, DataSource, T, IndexType>;
    };
};
 
enum class KDTreeSingleIndexAdaptorFlags
{
    None = 0,
    SkipInitialBuildIndex = 1
};
 
inline std::underlying_type<KDTreeSingleIndexAdaptorFlags>::type operator&(KDTreeSingleIndexAdaptorFlags lhs,
                                                                           KDTreeSingleIndexAdaptorFlags rhs)
{
    using underlying = typename std::underlying_type<KDTreeSingleIndexAdaptorFlags>::type;
    return static_cast<underlying>(lhs) & static_cast<underlying>(rhs);
}
 
struct KDTreeSingleIndexAdaptorParams
{
    KDTreeSingleIndexAdaptorParams(size_t _leaf_max_size = 10,
                                   KDTreeSingleIndexAdaptorFlags _flags = KDTreeSingleIndexAdaptorFlags::None)
        : leaf_max_size(_leaf_max_size), flags(_flags)
    {
    }
 
    size_t leaf_max_size;
    KDTreeSingleIndexAdaptorFlags flags;
};
 
struct SearchParameters
{
    SearchParameters(float eps_ = 0, bool sorted_ = true) : eps(eps_), sorted(sorted_) {}
 
    float eps;   
    bool sorted; 
};
class PooledAllocator
{
    static constexpr size_t WORDSIZE = 16;
    static constexpr size_t BLOCKSIZE = 8192;
 
    /* We maintain memory alignment to word boundaries by requiring that all
        allocations be in multiples of the machine wordsize.  */
    /* Size of machine word in bytes.  Must be power of 2. */
    /* Minimum number of bytes requested at a time from the system.  Must be
     * multiple of WORDSIZE. */
 
    using Offset = uint32_t;
    using Size = uint32_t;
    using Dimension = int32_t;
 
    Size remaining_ = 0;   
    void* base_ = nullptr; 
    void* loc_ = nullptr;  
 
    void internal_init()
    {
        remaining_ = 0;
        base_ = nullptr;
        usedMemory = 0;
        wastedMemory = 0;
    }
 
  public:
    Size usedMemory = 0;
    Size wastedMemory = 0;
 
    PooledAllocator() { internal_init(); }
 
    ~PooledAllocator() { free_all(); }
 
    void free_all()
    {
        while (base_ != nullptr)
        {
            // Get pointer to prev block
            void* prev = *(static_cast<void**>(base_));
            ::free(base_);
            base_ = prev;
        }
        internal_init();
    }
 
    void* malloc(const size_t req_size)
    {
        /* Round size up to a multiple of wordsize.  The following expression
            only works for WORDSIZE that is a power of 2, by masking last bits
           of incremented size to zero.
         */
        const Size size = (req_size + (WORDSIZE - 1)) & ~(WORDSIZE - 1);
 
        /* Check whether a new block must be allocated.  Note that the first
           word of a block is reserved for a pointer to the previous block.
         */
        if (size > remaining_)
        {
            wastedMemory += remaining_;
 
            /* Allocate new storage. */
            const Size blocksize = (size + sizeof(void*) + (WORDSIZE - 1) > BLOCKSIZE)
                                           ? size + sizeof(void*) + (WORDSIZE - 1)
                                           : BLOCKSIZE;
 
            // use the standard C malloc to allocate memory
            void* m = ::malloc(blocksize);
            if (!m)
            {
                fprintf(stderr, "Failed to allocate memory.\n");
                throw std::bad_alloc();
            }
 
            /* Fill first word of new block with pointer to previous block. */
            static_cast<void**>(m)[0] = base_;
            base_ = m;
 
            Size shift = 0;
            // int size_t = (WORDSIZE - ( (((size_t)m) + sizeof(void*)) &
            // (WORDSIZE-1))) & (WORDSIZE-1);
 
            remaining_ = blocksize - sizeof(void*) - shift;
            loc_ = (static_cast<char*>(m) + sizeof(void*) + shift);
        }
        void* rloc = loc_;
        loc_ = static_cast<char*>(loc_) + size;
        remaining_ -= size;
 
        usedMemory += size;
 
        return rloc;
    }
 
    template <typename T> T* allocate(const size_t count = 1)
    {
        T* mem = static_cast<T*>(this->malloc(sizeof(T) * count));
        return mem;
    }
};
template <int32_t DIM, typename T> struct array_or_vector
{
    using type = std::array<T, DIM>;
};
template <typename T> struct array_or_vector<-1, T>
{
    using type = std::vector<T>;
};
 
template <class Derived, typename Distance, class DatasetAdaptor, int32_t DIM = -1, typename IndexType = uint32_t>
class KDTreeBaseClass
{
  public:
    void freeIndex(Derived& obj)
    {
        obj.pool_.free_all();
        obj.root_node_ = nullptr;
        obj.size_at_index_build_ = 0;
    }
 
    using ElementType = typename Distance::ElementType;
    using DistanceType = typename Distance::DistanceType;
 
    std::vector<IndexType> vAcc_;
 
    using Offset = typename decltype(vAcc_)::size_type;
    using Size = typename decltype(vAcc_)::size_type;
    using Dimension = int32_t;
 
    /*---------------------------
     * Internal Data Structures
     * --------------------------*/
    struct Node
    {
        union {
            struct leaf
            {
                Offset left, right; 
            } lr;
            struct nonleaf
            {
                Dimension divfeat; 
                DistanceType divlow, divhigh;
            } sub;
        } node_type;
 
        Node *child1 = nullptr, *child2 = nullptr;
    };
 
    using NodePtr = Node*;
    using NodeConstPtr = const Node*;
 
    struct Interval
    {
        ElementType low, high;
    };
 
    NodePtr root_node_ = nullptr;
 
    Size leaf_max_size_ = 0;
 
    Size size_ = 0;
    Size size_at_index_build_ = 0;
    Dimension dim_ = 0; 
 
    using BoundingBox = typename array_or_vector<DIM, Interval>::type;
 
    using distance_vector_t = typename array_or_vector<DIM, DistanceType>::type;
 
    BoundingBox root_bbox_;
 
    PooledAllocator pool_;
 
    Size size(const Derived& obj) const { return obj.size_; }
 
    Size veclen(const Derived& obj) { return DIM > 0 ? DIM : obj.dim; }
 
    ElementType dataset_get(const Derived& obj, IndexType element, Dimension component) const
    {
        return obj.dataset_.kdtree_get_pt(element, component);
    }
 
    Size usedMemory(Derived& obj)
    {
        return obj.pool_.usedMemory + obj.pool_.wastedMemory +
               obj.dataset_.kdtree_get_point_count() * sizeof(IndexType); // pool memory and vind array memory
    }
 
    void computeMinMax(const Derived& obj, Offset ind, Size count, Dimension element, ElementType& min_elem,
                       ElementType& max_elem)
    {
        min_elem = dataset_get(obj, vAcc_[ind], element);
        max_elem = min_elem;
        for (Offset i = 1; i < count; ++i)
        {
            ElementType val = dataset_get(obj, vAcc_[ind + i], element);
            if (val < min_elem)
                min_elem = val;
            if (val > max_elem)
                max_elem = val;
        }
    }
 
    NodePtr divideTree(Derived& obj, const Offset left, const Offset right, BoundingBox& bbox)
    {
        NodePtr node = obj.pool_.template allocate<Node>(); // allocate memory
        const auto dims = (DIM > 0 ? DIM : obj.dim_);
 
        /* If too few exemplars remain, then make this a leaf node. */
        if ((right - left) <= static_cast<Offset>(obj.leaf_max_size_))
        {
            node->child1 = node->child2 = nullptr; /* Mark as leaf node. */
            node->node_type.lr.left = left;
            node->node_type.lr.right = right;
 
            // compute bounding-box of leaf points
            for (Dimension i = 0; i < dims; ++i)
            {
                bbox[i].low = dataset_get(obj, obj.vAcc_[left], i);
                bbox[i].high = dataset_get(obj, obj.vAcc_[left], i);
            }
            for (Offset k = left + 1; k < right; ++k)
            {
                for (Dimension i = 0; i < dims; ++i)
                {
                    const auto val = dataset_get(obj, obj.vAcc_[k], i);
                    if (bbox[i].low > val)
                        bbox[i].low = val;
                    if (bbox[i].high < val)
                        bbox[i].high = val;
                }
            }
        }
        else
        {
            Offset idx;
            Dimension cutfeat;
            DistanceType cutval;
            middleSplit_(obj, left, right - left, idx, cutfeat, cutval, bbox);
 
            node->node_type.sub.divfeat = cutfeat;
 
            BoundingBox left_bbox(bbox);
            left_bbox[cutfeat].high = cutval;
            node->child1 = this->divideTree(obj, left, left + idx, left_bbox);
 
            BoundingBox right_bbox(bbox);
            right_bbox[cutfeat].low = cutval;
            node->child2 = this->divideTree(obj, left + idx, right, right_bbox);
 
            node->node_type.sub.divlow = left_bbox[cutfeat].high;
            node->node_type.sub.divhigh = right_bbox[cutfeat].low;
 
            for (Dimension i = 0; i < dims; ++i)
            {
                bbox[i].low = std::min(left_bbox[i].low, right_bbox[i].low);
                bbox[i].high = std::max(left_bbox[i].high, right_bbox[i].high);
            }
        }
 
        return node;
    }
 
    void middleSplit_(const Derived& obj, const Offset ind, const Size count, Offset& index, Dimension& cutfeat,
                      DistanceType& cutval, const BoundingBox& bbox)
    {
        const auto dims = (DIM > 0 ? DIM : obj.dim_);
        const auto EPS = static_cast<DistanceType>(0.00001);
        ElementType max_span = bbox[0].high - bbox[0].low;
        for (Dimension i = 1; i < dims; ++i)
        {
            ElementType span = bbox[i].high - bbox[i].low;
            if (span > max_span)
            {
                max_span = span;
            }
        }
        ElementType max_spread = -1;
        cutfeat = 0;
        for (Dimension i = 0; i < dims; ++i)
        {
            ElementType span = bbox[i].high - bbox[i].low;
            if (span > (1 - EPS) * max_span)
            {
                ElementType min_elem, max_elem;
                computeMinMax(obj, ind, count, i, min_elem, max_elem);
                ElementType spread = max_elem - min_elem;
                if (spread > max_spread)
                {
                    cutfeat = i;
                    max_spread = spread;
                }
            }
        }
        // split in the middle
        DistanceType split_val = (bbox[cutfeat].low + bbox[cutfeat].high) / 2;
        ElementType min_elem, max_elem;
        computeMinMax(obj, ind, count, cutfeat, min_elem, max_elem);
 
        if (split_val < min_elem)
            cutval = min_elem;
        else if (split_val > max_elem)
            cutval = max_elem;
        else
            cutval = split_val;
 
        Offset lim1, lim2;
        planeSplit(obj, ind, count, cutfeat, cutval, lim1, lim2);
 
        if (lim1 > count / 2)
            index = lim1;
        else if (lim2 < count / 2)
            index = lim2;
        else
            index = count / 2;
    }
 
    void planeSplit(const Derived& obj, const Offset ind, const Size count, const Dimension cutfeat,
                    const DistanceType& cutval, Offset& lim1, Offset& lim2)
    {
        /* Move vector indices for left subtree to front of list. */
        Offset left = 0;
        Offset right = count - 1;
        for (;;)
        {
            while (left <= right && dataset_get(obj, vAcc_[ind + left], cutfeat) < cutval)
                ++left;
            while (right && left <= right && dataset_get(obj, vAcc_[ind + right], cutfeat) >= cutval)
                --right;
            if (left > right || !right)
                break; // "!right" was added to support unsigned Index types
            std::swap(vAcc_[ind + left], vAcc_[ind + right]);
            ++left;
            --right;
        }
        /* If either list is empty, it means that all remaining features
         * are identical. Split in the middle to maintain a balanced tree.
         */
        lim1 = left;
        right = count - 1;
        for (;;)
        {
            while (left <= right && dataset_get(obj, vAcc_[ind + left], cutfeat) <= cutval)
                ++left;
            while (right && left <= right && dataset_get(obj, vAcc_[ind + right], cutfeat) > cutval)
                --right;
            if (left > right || !right)
                break; // "!right" was added to support unsigned Index types
            std::swap(vAcc_[ind + left], vAcc_[ind + right]);
            ++left;
            --right;
        }
        lim2 = left;
    }
 
    DistanceType computeInitialDistances(const Derived& obj, const ElementType* vec, distance_vector_t& dists) const
    {
        assert(vec);
        DistanceType dist = DistanceType();
 
        for (Dimension i = 0; i < (DIM > 0 ? DIM : obj.dim_); ++i)
        {
            if (vec[i] < obj.root_bbox_[i].low)
            {
                dists[i] = obj.distance_.accum_dist(vec[i], obj.root_bbox_[i].low, i);
                dist += dists[i];
            }
            if (vec[i] > obj.root_bbox_[i].high)
            {
                dists[i] = obj.distance_.accum_dist(vec[i], obj.root_bbox_[i].high, i);
                dist += dists[i];
            }
        }
        return dist;
    }
 
    static void save_tree(const Derived& obj, std::ostream& stream, const NodeConstPtr tree)
    {
        save_value(stream, *tree);
        if (tree->child1 != nullptr)
        {
            save_tree(obj, stream, tree->child1);
        }
        if (tree->child2 != nullptr)
        {
            save_tree(obj, stream, tree->child2);
        }
    }
 
    static void load_tree(Derived& obj, std::istream& stream, NodePtr& tree)
    {
        tree = obj.pool_.template allocate<Node>();
        load_value(stream, *tree);
        if (tree->child1 != nullptr)
        {
            load_tree(obj, stream, tree->child1);
        }
        if (tree->child2 != nullptr)
        {
            load_tree(obj, stream, tree->child2);
        }
    }
 
    void saveIndex(const Derived& obj, std::ostream& stream) const
    {
        save_value(stream, obj.size_);
        save_value(stream, obj.dim_);
        save_value(stream, obj.root_bbox_);
        save_value(stream, obj.leaf_max_size_);
        save_value(stream, obj.vAcc_);
        save_tree(obj, stream, obj.root_node_);
    }
 
    void loadIndex(Derived& obj, std::istream& stream)
    {
        load_value(stream, obj.size_);
        load_value(stream, obj.dim_);
        load_value(stream, obj.root_bbox_);
        load_value(stream, obj.leaf_max_size_);
        load_value(stream, obj.vAcc_);
        load_tree(obj, stream, obj.root_node_);
    }
};
 
template <typename Distance, class DatasetAdaptor, int32_t DIM = -1, typename IndexType = uint32_t>
class KDTreeSingleIndexAdaptor
    : public KDTreeBaseClass<KDTreeSingleIndexAdaptor<Distance, DatasetAdaptor, DIM, IndexType>, Distance,
                             DatasetAdaptor, DIM, IndexType>
{
  public:
    explicit KDTreeSingleIndexAdaptor(const KDTreeSingleIndexAdaptor<Distance, DatasetAdaptor, DIM, IndexType>&) =
            delete;
 
    const DatasetAdaptor& dataset_;
 
    const KDTreeSingleIndexAdaptorParams indexParams;
 
    Distance distance_;
 
    using Base = typename nanoflann::KDTreeBaseClass<
            nanoflann::KDTreeSingleIndexAdaptor<Distance, DatasetAdaptor, DIM, IndexType>, Distance, DatasetAdaptor,
            DIM, IndexType>;
 
    using Offset = typename Base::Offset;
    using Size = typename Base::Size;
    using Dimension = typename Base::Dimension;
 
    using ElementType = typename Base::ElementType;
    using DistanceType = typename Base::DistanceType;
 
    using Node = typename Base::Node;
    using NodePtr = Node*;
 
    using Interval = typename Base::Interval;
 
    using BoundingBox = typename Base::BoundingBox;
 
    using distance_vector_t = typename Base::distance_vector_t;
 
    template <class... Args>
    explicit KDTreeSingleIndexAdaptor(const Dimension dimensionality, const DatasetAdaptor& inputData,
                                      const KDTreeSingleIndexAdaptorParams& params, Args&&... args)
        : dataset_(inputData), indexParams(params), distance_(inputData, std::forward<Args>(args)...)
    {
        init(dimensionality, params);
    }
 
    explicit KDTreeSingleIndexAdaptor(const Dimension dimensionality, const DatasetAdaptor& inputData,
                                      const KDTreeSingleIndexAdaptorParams& params = {})
        : dataset_(inputData), indexParams(params), distance_(inputData)
    {
        init(dimensionality, params);
    }
 
  private:
    void init(const Dimension dimensionality, const KDTreeSingleIndexAdaptorParams& params)
    {
        Base::size_ = dataset_.kdtree_get_point_count();
        Base::size_at_index_build_ = Base::size_;
        Base::dim_ = dimensionality;
        if (DIM > 0)
            Base::dim_ = DIM;
        Base::leaf_max_size_ = params.leaf_max_size;
 
        if (!(params.flags & KDTreeSingleIndexAdaptorFlags::SkipInitialBuildIndex))
        {
            // Build KD-tree:
            buildIndex();
        }
    }
 
  public:
    void buildIndex()
    {
        Base::size_ = dataset_.kdtree_get_point_count();
        Base::size_at_index_build_ = Base::size_;
        init_vind();
        this->freeIndex(*this);
        Base::size_at_index_build_ = Base::size_;
        if (Base::size_ == 0)
            return;
        computeBoundingBox(Base::root_bbox_);
        // construct the tree
        Base::root_node_ = this->divideTree(*this, 0, Base::size_, Base::root_bbox_);
    }
 
    template <typename RESULTSET>
    bool findNeighbors(RESULTSET& result, const ElementType* vec, const SearchParameters& searchParams = {}) const
    {
        assert(vec);
        if (this->size(*this) == 0)
            return false;
        if (!Base::root_node_)
            throw std::runtime_error("[nanoflann] findNeighbors() called before building the "
                                     "index.");
        float epsError = 1 + searchParams.eps;
 
        // fixed or variable-sized container (depending on DIM)
        distance_vector_t dists;
        // Fill it with zeros.
        auto zero = static_cast<decltype(result.worstDist())>(0);
        assign(dists, (DIM > 0 ? DIM : Base::dim_), zero);
        DistanceType dist = this->computeInitialDistances(*this, vec, dists);
        searchLevel(result, vec, Base::root_node_, dist, dists, epsError);
        return result.full();
    }
 
    Size knnSearch(const ElementType* query_point, const Size num_closest, IndexType* out_indices,
                   DistanceType* out_distances) const
    {
        nanoflann::KNNResultSet<DistanceType, IndexType> resultSet(num_closest);
        resultSet.init(out_indices, out_distances);
        findNeighbors(resultSet, query_point);
        return resultSet.size();
    }
 
    Size radiusSearch(const ElementType* query_point, const DistanceType& radius,
                      std::vector<ResultItem<IndexType, DistanceType>>& IndicesDists,
                      const SearchParameters& searchParams = {}) const
    {
        RadiusResultSet<DistanceType, IndexType> resultSet(radius, IndicesDists);
        const Size nFound = radiusSearchCustomCallback(query_point, resultSet, searchParams);
        if (searchParams.sorted)
            std::sort(IndicesDists.begin(), IndicesDists.end(), IndexDist_Sorter());
        return nFound;
    }
 
    template <class SEARCH_CALLBACK>
    Size radiusSearchCustomCallback(const ElementType* query_point, SEARCH_CALLBACK& resultSet,
                                    const SearchParameters& searchParams = {}) const
    {
        findNeighbors(resultSet, query_point, searchParams);
        return resultSet.size();
    }
 
  public:
    void init_vind()
    {
        // Create a permutable array of indices to the input vectors.
        Base::size_ = dataset_.kdtree_get_point_count();
        if (Base::vAcc_.size() != Base::size_)
            Base::vAcc_.resize(Base::size_);
        for (Size i = 0; i < Base::size_; i++)
            Base::vAcc_[i] = i;
    }
 
    void computeBoundingBox(BoundingBox& bbox)
    {
        const auto dims = (DIM > 0 ? DIM : Base::dim_);
        resize(bbox, dims);
        if (dataset_.kdtree_get_bbox(bbox))
        {
            // Done! It was implemented in derived class
        }
        else
        {
            const Size N = dataset_.kdtree_get_point_count();
            if (!N)
                throw std::runtime_error("[nanoflann] computeBoundingBox() called but "
                                         "no data points found.");
            for (Dimension i = 0; i < dims; ++i)
            {
                bbox[i].low = bbox[i].high = this->dataset_get(*this, Base::vAcc_[0], i);
            }
            for (Offset k = 1; k < N; ++k)
            {
                for (Dimension i = 0; i < dims; ++i)
                {
                    const auto val = this->dataset_get(*this, Base::vAcc_[k], i);
                    if (val < bbox[i].low)
                        bbox[i].low = val;
                    if (val > bbox[i].high)
                        bbox[i].high = val;
                }
            }
        }
    }
 
    template <class RESULTSET>
    bool searchLevel(RESULTSET& result_set, const ElementType* vec, const NodePtr node, DistanceType mindist,
                     distance_vector_t& dists, const float epsError) const
    {
        /* If this is a leaf node, then do check and return. */
        if ((node->child1 == nullptr) && (node->child2 == nullptr))
        {
            DistanceType worst_dist = result_set.worstDist();
            for (Offset i = node->node_type.lr.left; i < node->node_type.lr.right; ++i)
            {
                const IndexType accessor = Base::vAcc_[i]; // reorder... : i;
                DistanceType dist = distance_.evalMetric(vec, accessor, (DIM > 0 ? DIM : Base::dim_));
                if (dist < worst_dist)
                {
                    if (!result_set.addPoint(dist, Base::vAcc_[i]))
                    {
                        // the resultset doesn't want to receive any more
                        // points, we're done searching!
                        return false;
                    }
                }
            }
            return true;
        }
 
        /* Which child branch should be taken first? */
        Dimension idx = node->node_type.sub.divfeat;
        ElementType val = vec[idx];
        DistanceType diff1 = val - node->node_type.sub.divlow;
        DistanceType diff2 = val - node->node_type.sub.divhigh;
 
        NodePtr bestChild;
        NodePtr otherChild;
        DistanceType cut_dist;
        if ((diff1 + diff2) < 0)
        {
            bestChild = node->child1;
            otherChild = node->child2;
            cut_dist = distance_.accum_dist(val, node->node_type.sub.divhigh, idx);
        }
        else
        {
            bestChild = node->child2;
            otherChild = node->child1;
            cut_dist = distance_.accum_dist(val, node->node_type.sub.divlow, idx);
        }
 
        /* Call recursively to search next level down. */
        if (!searchLevel(result_set, vec, bestChild, mindist, dists, epsError))
        {
            // the resultset doesn't want to receive any more points, we're done
            // searching!
            return false;
        }
 
        DistanceType dst = dists[idx];
        mindist = mindist + cut_dist - dst;
        dists[idx] = cut_dist;
        if (mindist * epsError <= result_set.worstDist())
        {
            if (!searchLevel(result_set, vec, otherChild, mindist, dists, epsError))
            {
                // the resultset doesn't want to receive any more points, we're
                // done searching!
                return false;
            }
        }
        dists[idx] = dst;
        return true;
    }
 
  public:
    void saveIndex(std::ostream& stream) const { Base::saveIndex(*this, stream); }
 
    void loadIndex(std::istream& stream) { Base::loadIndex(*this, stream); }
 
}; // class KDTree
 
template <typename Distance, class DatasetAdaptor, int32_t DIM = -1, typename IndexType = uint32_t>
class KDTreeSingleIndexDynamicAdaptor_
    : public KDTreeBaseClass<KDTreeSingleIndexDynamicAdaptor_<Distance, DatasetAdaptor, DIM, IndexType>, Distance,
                             DatasetAdaptor, DIM, IndexType>
{
  public:
    const DatasetAdaptor& dataset_; 
 
    KDTreeSingleIndexAdaptorParams index_params_;
 
    std::vector<int>& treeIndex_;
 
    Distance distance_;
 
    using Base = typename nanoflann::KDTreeBaseClass<
            nanoflann::KDTreeSingleIndexDynamicAdaptor_<Distance, DatasetAdaptor, DIM, IndexType>, Distance,
            DatasetAdaptor, DIM, IndexType>;
 
    using ElementType = typename Base::ElementType;
    using DistanceType = typename Base::DistanceType;
 
    using Offset = typename Base::Offset;
    using Size = typename Base::Size;
    using Dimension = typename Base::Dimension;
 
    using Node = typename Base::Node;
    using NodePtr = Node*;
 
    using Interval = typename Base::Interval;
    using BoundingBox = typename Base::BoundingBox;
 
    using distance_vector_t = typename Base::distance_vector_t;
 
    KDTreeSingleIndexDynamicAdaptor_(const Dimension dimensionality, const DatasetAdaptor& inputData,
                                     std::vector<int>& treeIndex,
                                     const KDTreeSingleIndexAdaptorParams& params = KDTreeSingleIndexAdaptorParams())
        : dataset_(inputData), index_params_(params), treeIndex_(treeIndex), distance_(inputData)
    {
        Base::size_ = 0;
        Base::size_at_index_build_ = 0;
        for (auto& v : Base::root_bbox_)
            v = {};
        Base::dim_ = dimensionality;
        if (DIM > 0)
            Base::dim_ = DIM;
        Base::leaf_max_size_ = params.leaf_max_size;
    }
 
    KDTreeSingleIndexDynamicAdaptor_(const KDTreeSingleIndexDynamicAdaptor_& rhs) = default;
 
    KDTreeSingleIndexDynamicAdaptor_ operator=(const KDTreeSingleIndexDynamicAdaptor_& rhs)
    {
        KDTreeSingleIndexDynamicAdaptor_ tmp(rhs);
        std::swap(Base::vAcc_, tmp.Base::vAcc_);
        std::swap(Base::leaf_max_size_, tmp.Base::leaf_max_size_);
        std::swap(index_params_, tmp.index_params_);
        std::swap(treeIndex_, tmp.treeIndex_);
        std::swap(Base::size_, tmp.Base::size_);
        std::swap(Base::size_at_index_build_, tmp.Base::size_at_index_build_);
        std::swap(Base::root_node_, tmp.Base::root_node_);
        std::swap(Base::root_bbox_, tmp.Base::root_bbox_);
        std::swap(Base::pool_, tmp.Base::pool_);
        return *this;
    }
 
    void buildIndex()
    {
        Base::size_ = Base::vAcc_.size();
        this->freeIndex(*this);
        Base::size_at_index_build_ = Base::size_;
        if (Base::size_ == 0)
            return;
        computeBoundingBox(Base::root_bbox_);
        // construct the tree
        Base::root_node_ = this->divideTree(*this, 0, Base::size_, Base::root_bbox_);
    }
 
    template <typename RESULTSET>
    bool findNeighbors(RESULTSET& result, const ElementType* vec, const SearchParameters& searchParams = {}) const
    {
        assert(vec);
        if (this->size(*this) == 0)
            return false;
        if (!Base::root_node_)
            return false;
        float epsError = 1 + searchParams.eps;
 
        // fixed or variable-sized container (depending on DIM)
        distance_vector_t dists;
        // Fill it with zeros.
        assign(dists, (DIM > 0 ? DIM : Base::dim_), static_cast<typename distance_vector_t::value_type>(0));
        DistanceType dist = this->computeInitialDistances(*this, vec, dists);
        searchLevel(result, vec, Base::root_node_, dist, dists, epsError);
        return result.full();
    }
 
    Size knnSearch(const ElementType* query_point, const Size num_closest, IndexType* out_indices,
                   DistanceType* out_distances) const
    {
        nanoflann::KNNResultSet<DistanceType, IndexType> resultSet(num_closest);
        resultSet.init(out_indices, out_distances);
        findNeighbors(resultSet, query_point);
        return resultSet.size();
    }
 
    Size radiusSearch(const ElementType* query_point, const DistanceType& radius,
                      std::vector<ResultItem<IndexType, DistanceType>>& IndicesDists,
                      const SearchParameters& searchParams = {}) const
    {
        RadiusResultSet<DistanceType, IndexType> resultSet(radius, IndicesDists);
        const size_t nFound = radiusSearchCustomCallback(query_point, resultSet, searchParams);
        if (searchParams.sorted)
            std::sort(IndicesDists.begin(), IndicesDists.end(), IndexDist_Sorter());
        return nFound;
    }
 
    template <class SEARCH_CALLBACK>
    Size radiusSearchCustomCallback(const ElementType* query_point, SEARCH_CALLBACK& resultSet,
                                    const SearchParameters& searchParams = {}) const
    {
        findNeighbors(resultSet, query_point, searchParams);
        return resultSet.size();
    }
 
  public:
    void computeBoundingBox(BoundingBox& bbox)
    {
        const auto dims = (DIM > 0 ? DIM : Base::dim_);
        resize(bbox, dims);
 
        if (dataset_.kdtree_get_bbox(bbox))
        {
            // Done! It was implemented in derived class
        }
        else
        {
            const Size N = Base::size_;
            if (!N)
                throw std::runtime_error("[nanoflann] computeBoundingBox() called but "
                                         "no data points found.");
            for (Dimension i = 0; i < dims; ++i)
            {
                bbox[i].low = bbox[i].high = this->dataset_get(*this, Base::vAcc_[0], i);
            }
            for (Offset k = 1; k < N; ++k)
            {
                for (Dimension i = 0; i < dims; ++i)
                {
                    const auto val = this->dataset_get(*this, Base::vAcc_[k], i);
                    if (val < bbox[i].low)
                        bbox[i].low = val;
                    if (val > bbox[i].high)
                        bbox[i].high = val;
                }
            }
        }
    }
 
    template <class RESULTSET>
    void searchLevel(RESULTSET& result_set, const ElementType* vec, const NodePtr node, DistanceType mindist,
                     distance_vector_t& dists, const float epsError) const
    {
        /* If this is a leaf node, then do check and return. */
        if ((node->child1 == nullptr) && (node->child2 == nullptr))
        {
            DistanceType worst_dist = result_set.worstDist();
            for (Offset i = node->node_type.lr.left; i < node->node_type.lr.right; ++i)
            {
                const IndexType index = Base::vAcc_[i]; // reorder... : i;
                if (treeIndex_[index] == -1)
                    continue;
                DistanceType dist = distance_.evalMetric(vec, index, (DIM > 0 ? DIM : Base::dim_));
                if (dist < worst_dist)
                {
                    if (!result_set.addPoint(static_cast<typename RESULTSET::DistanceType>(dist),
                                             static_cast<typename RESULTSET::IndexType>(Base::vAcc_[i])))
                    {
                        // the resultset doesn't want to receive any more
                        // points, we're done searching!
                        return; // false;
                    }
                }
            }
            return;
        }
 
        /* Which child branch should be taken first? */
        Dimension idx = node->node_type.sub.divfeat;
        ElementType val = vec[idx];
        DistanceType diff1 = val - node->node_type.sub.divlow;
        DistanceType diff2 = val - node->node_type.sub.divhigh;
 
        NodePtr bestChild;
        NodePtr otherChild;
        DistanceType cut_dist;
        if ((diff1 + diff2) < 0)
        {
            bestChild = node->child1;
            otherChild = node->child2;
            cut_dist = distance_.accum_dist(val, node->node_type.sub.divhigh, idx);
        }
        else
        {
            bestChild = node->child2;
            otherChild = node->child1;
            cut_dist = distance_.accum_dist(val, node->node_type.sub.divlow, idx);
        }
 
        /* Call recursively to search next level down. */
        searchLevel(result_set, vec, bestChild, mindist, dists, epsError);
 
        DistanceType dst = dists[idx];
        mindist = mindist + cut_dist - dst;
        dists[idx] = cut_dist;
        if (mindist * epsError <= result_set.worstDist())
        {
            searchLevel(result_set, vec, otherChild, mindist, dists, epsError);
        }
        dists[idx] = dst;
    }
 
  public:
    void saveIndex(std::ostream& stream) { saveIndex(*this, stream); }
 
    void loadIndex(std::istream& stream) { loadIndex(*this, stream); }
};
 
template <typename Distance, class DatasetAdaptor, int32_t DIM = -1, typename IndexType = uint32_t>
class KDTreeSingleIndexDynamicAdaptor
{
  public:
    using ElementType = typename Distance::ElementType;
    using DistanceType = typename Distance::DistanceType;
 
    using Offset = typename KDTreeSingleIndexDynamicAdaptor_<Distance, DatasetAdaptor, DIM>::Offset;
    using Size = typename KDTreeSingleIndexDynamicAdaptor_<Distance, DatasetAdaptor, DIM>::Size;
    using Dimension = typename KDTreeSingleIndexDynamicAdaptor_<Distance, DatasetAdaptor, DIM>::Dimension;
 
  protected:
    Size leaf_max_size_;
    Size treeCount_;
    Size pointCount_;
 
    const DatasetAdaptor& dataset_; 
 
    std::vector<int> treeIndex_;
    std::unordered_set<int> removedPoints_;
 
    KDTreeSingleIndexAdaptorParams index_params_;
 
    Dimension dim_; 
 
    using index_container_t = KDTreeSingleIndexDynamicAdaptor_<Distance, DatasetAdaptor, DIM, IndexType>;
    std::vector<index_container_t> index_;
 
  public:
    const std::vector<index_container_t>& getAllIndices() const { return index_; }
 
  private:
    int First0Bit(IndexType num)
    {
        int pos = 0;
        while (num & 1)
        {
            num = num >> 1;
            pos++;
        }
        return pos;
    }
 
    void init()
    {
        using my_kd_tree_t = KDTreeSingleIndexDynamicAdaptor_<Distance, DatasetAdaptor, DIM, IndexType>;
        std::vector<my_kd_tree_t> index(treeCount_, my_kd_tree_t(dim_ /*dim*/, dataset_, treeIndex_, index_params_));
        index_ = index;
    }
 
  public:
    Distance distance_;
 
    explicit KDTreeSingleIndexDynamicAdaptor(
            const int dimensionality, const DatasetAdaptor& inputData,
            const KDTreeSingleIndexAdaptorParams& params = KDTreeSingleIndexAdaptorParams(),
            const size_t maximumPointCount = 1000000000U)
        : dataset_(inputData), index_params_(params), distance_(inputData)
    {
        treeCount_ = static_cast<size_t>(std::log2(maximumPointCount)) + 1;
        pointCount_ = 0U;
        dim_ = dimensionality;
        treeIndex_.clear();
        if (DIM > 0)
            dim_ = DIM;
        leaf_max_size_ = params.leaf_max_size;
        init();
        const size_t num_initial_points = dataset_.kdtree_get_point_count();
        if (num_initial_points > 0)
        {
            addPoints(0, num_initial_points - 1);
        }
    }
 
    explicit KDTreeSingleIndexDynamicAdaptor(
            const KDTreeSingleIndexDynamicAdaptor<Distance, DatasetAdaptor, DIM, IndexType>&) = delete;
 
    void addPoints(IndexType start, IndexType end)
    {
        const Size count = end - start + 1;
        int maxIndex = 0;
        treeIndex_.resize(treeIndex_.size() + count);
        for (IndexType idx = start; idx <= end; idx++)
        {
            const int pos = First0Bit(pointCount_);
            maxIndex = std::max(pos, maxIndex);
            treeIndex_[pointCount_] = pos;
 
            const auto it = removedPoints_.find(idx);
            if (it != removedPoints_.end())
            {
                removedPoints_.erase(it);
                treeIndex_[idx] = pos;
            }
 
            for (int i = 0; i < pos; i++)
            {
                for (int j = 0; j < static_cast<int>(index_[i].vAcc_.size()); j++)
                {
                    index_[pos].vAcc_.push_back(index_[i].vAcc_[j]);
                    if (treeIndex_[index_[i].vAcc_[j]] != -1)
                        treeIndex_[index_[i].vAcc_[j]] = pos;
                }
                index_[i].vAcc_.clear();
            }
            index_[pos].vAcc_.push_back(idx);
            pointCount_++;
        }
 
        for (int i = 0; i <= maxIndex; ++i)
        {
            index_[i].freeIndex(index_[i]);
            if (!index_[i].vAcc_.empty())
                index_[i].buildIndex();
        }
    }
 
    void removePoint(size_t idx)
    {
        if (idx >= pointCount_)
            return;
        removedPoints_.insert(idx);
        treeIndex_[idx] = -1;
    }
 
    template <typename RESULTSET>
    bool findNeighbors(RESULTSET& result, const ElementType* vec, const SearchParameters& searchParams = {}) const
    {
        for (size_t i = 0; i < treeCount_; i++)
        {
            index_[i].findNeighbors(result, &vec[0], searchParams);
        }
        return result.full();
    }
};
 
template <class MatrixType, int32_t DIM = -1, class Distance = nanoflann::metric_L2, bool row_major = true>
struct KDTreeEigenMatrixAdaptor
{
    using self_t = KDTreeEigenMatrixAdaptor<MatrixType, DIM, Distance, row_major>;
    using num_t = typename MatrixType::Scalar;
    using IndexType = typename MatrixType::Index;
    using metric_t = typename Distance::template traits<num_t, self_t, IndexType>::distance_t;
 
    using index_t = KDTreeSingleIndexAdaptor<
            metric_t, self_t, row_major ? MatrixType::ColsAtCompileTime : MatrixType::RowsAtCompileTime, IndexType>;
 
    index_t* index_; 
 
    using Offset = typename index_t::Offset;
    using Size = typename index_t::Size;
    using Dimension = typename index_t::Dimension;
 
    explicit KDTreeEigenMatrixAdaptor(const Dimension dimensionality,
                                      const std::reference_wrapper<const MatrixType>& mat, const int leaf_max_size = 10)
        : m_data_matrix(mat)
    {
        const auto dims = row_major ? mat.get().cols() : mat.get().rows();
        if (static_cast<Dimension>(dims) != dimensionality)
            throw std::runtime_error("Error: 'dimensionality' must match column count in data "
                                     "matrix");
        if (DIM > 0 && static_cast<int32_t>(dims) != DIM)
            throw std::runtime_error("Data set dimensionality does not match the 'DIM' template "
                                     "argument");
        index_ = new index_t(dims, *this /* adaptor */, nanoflann::KDTreeSingleIndexAdaptorParams(leaf_max_size));
    }
 
  public:
    KDTreeEigenMatrixAdaptor(const self_t&) = delete;
 
    ~KDTreeEigenMatrixAdaptor() { delete index_; }
 
    const std::reference_wrapper<const MatrixType> m_data_matrix;
 
    void query(const num_t* query_point, const Size num_closest, IndexType* out_indices, num_t* out_distances) const
    {
        nanoflann::KNNResultSet<num_t, IndexType> resultSet(num_closest);
        resultSet.init(out_indices, out_distances);
        index_->findNeighbors(resultSet, query_point);
    }
 
    const self_t& derived() const { return *this; }
    self_t& derived() { return *this; }
 
    // Must return the number of data points
    Size kdtree_get_point_count() const
    {
        if (row_major)
            return m_data_matrix.get().rows();
        else
            return m_data_matrix.get().cols();
    }
 
    // Returns the dim'th component of the idx'th point in the class:
    num_t kdtree_get_pt(const IndexType idx, size_t dim) const
    {
        if (row_major)
            return m_data_matrix.get().coeff(idx, IndexType(dim));
        else
            return m_data_matrix.get().coeff(IndexType(dim), idx);
    }
 
    // Optional bounding-box computation: return false to default to a standard
    // bbox computation loop.
    //   Return true if the BBOX was already computed by the class and returned
    //   in "bb" so it can be avoided to redo it again. Look at bb.size() to
    //   find out the expected dimensionality (e.g. 2 or 3 for point clouds)
    template <class BBOX> bool kdtree_get_bbox(BBOX& /*bb*/) const { return false; }
 
}; // end of KDTreeEigenMatrixAdaptor
 // end of grouping
} // namespace nanoflann