heap.h

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 *
 * 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.
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#ifndef FLANN_HEAP_H_
#define FLANN_HEAP_H_
 
#include <algorithm>
#include <vector>
 
namespace flann
{
 
template <typename T>
class Heap
{
 
    std::vector<T> heap;
    int length;
 
    int count;
 
 
 
public:
    Heap(int size)
    {
        length = size;
        heap.reserve(length);
        count = 0;
    }
 
    int size()
    {
        return count;
    }
 
    bool empty()
    {
        return size()==0;
    }
 
    void clear()
    {
        heap.clear();
        count = 0;
    }
 
    // fix std::binary_function unrecognized error when set c++17
    // struct CompareT : public std::binary_function<T,T,bool>
    struct CompareT
    {
        bool operator()(const T& t_1, const T& t_2) const
        {
            return t_2 < t_1;
        }
    };
 
    void insert(const T& value)
    {
        /* If heap is full, then return without adding this element. */
        if (count == length) {
            return;
        }
 
        heap.push_back(value);
        static CompareT compareT;
        std::push_heap(heap.begin(), heap.end(), compareT);
        ++count;
    }
 
 
 
    bool popMin(T& value)
    {
        if (count == 0) {
            return false;
        }
 
        value = heap[0];
        static CompareT compareT;
        std::pop_heap(heap.begin(), heap.end(), compareT);
        heap.pop_back();
        --count;
 
        return true;  /* Return old last node. */
    }
};
 
 
template <typename T>
class IntervalHeap
{
    struct Interval
    {
        T left;
        T right;
    };
 
    std::vector<Interval> heap;
    size_t capacity_;
    size_t size_;
 
public:
    IntervalHeap(int capacity) : capacity_(capacity), size_(0)
    {
        heap.resize(capacity/2 + capacity%2 + 1); // 1-based indexing
    }
 
    size_t size()
    {
        return size_;
    }
 
    bool empty()
    {
        return size_==0;
    }
 
    void clear()
    {
        size_ = 0;
    }
 
    void insert(const T& value)
    {
        /* If heap is full, then return without adding this element. */
        if (size_ == capacity_) {
            return;
        }
 
        // insert into the root
        if (size_<2) {
            if (size_==0) {
                heap[1].left = value;
                heap[1].right = value;
            }
            else {
                if (value<heap[1].left) {
                    heap[1].left = value;
                }
                else {
                    heap[1].right = value;
                }
            }
            ++size_;
            return;
        }
 
        size_t last_pos = size_/2 + size_%2;
        bool min_heap;
 
        if (size_%2) { // odd number of elements
            min_heap = (value<heap[last_pos].left)? true : false;
        }
        else {
            ++last_pos;
            min_heap = (value<heap[last_pos/2].left)? true : false;
        }
 
        if (min_heap) {
            size_t pos = last_pos;
            size_t par = pos/2;
            while (pos>1 && value < heap[par].left) {
                heap[pos].left = heap[par].left;
                pos = par;
                par = pos/2;
            }
            heap[pos].left = value;
            ++size_;
 
            if (size_%2) { // duplicate element in last position if size is odd
                heap[last_pos].right = heap[last_pos].left;
            }
        }
        else {
            size_t pos = last_pos;
            size_t par = pos/2;
            while (pos>1 && heap[par].right < value) {
                heap[pos].right = heap[par].right;
                pos = par;
                par = pos/2;
            }
            heap[pos].right = value;
            ++size_;
 
            if (size_%2) { // duplicate element in last position if size is odd
                heap[last_pos].left = heap[last_pos].right;
            }
        }
    }
 
 
    bool popMin(T& value)
    {
        if (size_ == 0) {
            return false;
        }
 
        value = heap[1].left;
        size_t last_pos = size_/2 + size_%2;
        T elem = heap[last_pos].left;
 
        if (size_ % 2) { // odd number of elements
            --last_pos;
        }
        else {
            heap[last_pos].left = heap[last_pos].right;
        }
        --size_;
        if (size_<2) return true;
 
        size_t crt=1; // root node
        size_t child = crt*2;
 
        while (child <= last_pos) {
            if (child < last_pos && heap[child+1].left < heap[child].left) ++child; // pick the child with min
 
            if (!(heap[child].left<elem)) break;
 
            heap[crt].left = heap[child].left;
            if (heap[child].right<elem) {
                std::swap(elem, heap[child].right);
            }
 
            crt = child;
            child *= 2;
        }
        heap[crt].left = elem;
        return true;
    }
 
 
    bool popMax(T& value)
    {
        if (size_ == 0) {
            return false;
        }
 
        value = heap[1].right;
        size_t last_pos = size_/2 + size_%2;
        T elem = heap[last_pos].right;
 
        if (size_%2) { // odd number of elements
            --last_pos;
        }
        else {
            heap[last_pos].right = heap[last_pos].left;
        }
        --size_;
        if (size_<2) return true;
 
        size_t crt=1; // root node
        size_t child = crt*2;
 
        while (child <= last_pos) {
            if (child < last_pos && heap[child].right < heap[child+1].right) ++child; // pick the child with max
 
            if (!(elem < heap[child].right)) break;
 
            heap[crt].right = heap[child].right;
            if (elem<heap[child].left) {
                std::swap(elem, heap[child].left);
            }
 
            crt = child;
            child *= 2;
        }
        heap[crt].right = elem;
        return true;
    }
 
 
    bool getMin(T& value)
    {
        if (size_==0) {
            return false;
        }
        value = heap[1].left;
        return true;
    }
 
 
    bool getMax(T& value)
    {
        if (size_==0) {
            return false;
        }
        value = heap[1].right;
        return true;
    }
};
 
 
template <typename T>
class BoundedHeap
{
    IntervalHeap<T> interval_heap_;
    size_t capacity_;
public:
    BoundedHeap(size_t capacity) : interval_heap_(capacity), capacity_(capacity)
    {
 
    }
 
    int size()
    {
        return interval_heap_.size();
    }
 
    bool empty()
    {
        return interval_heap_.empty();
    }
 
    void clear()
    {
        interval_heap_.clear();
    }
 
    void insert(const T& value)
    {
        if (interval_heap_.size()==capacity_) {
            T max;
            interval_heap_.getMax(max);
            if (max<value) return;
            interval_heap_.popMax(max);
        }
        interval_heap_.insert(value);
    }
 
    bool popMin(T& value)
    {
        return interval_heap_.popMin(value);
    }
};
 
 
 
}
 
#endif //FLANN_HEAP_H_