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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.
 *
 * THE BSD LICENSE
 *
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 * 1. Redistributions of source code must retain the above copyright
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 *    notice, this list of conditions and the following disclaimer in the
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 *************************************************************************/

#ifndef OPENCV_FLANN_HEAP_H_
#define OPENCV_FLANN_HEAP_H_

#include <algorithm>
#include <vector>

namespace cvflann
{

/**
 * Priority Queue Implementation
 *
 * The priority queue is implemented with a heap.  A heap is a complete
 * (full) binary tree in which each parent is less than both of its
 * children, but the order of the children is unspecified.
 */
template <typename T>
class Heap
{

    /**
     * Storage array for the heap.
     * Type T must be comparable.
     */
    std::vector<T> heap;
    int length;

    /**
     * Number of element in the heap
     */
    int count;



public:
    /**
     * Constructor.
     *
     * Params:
     *     size = heap size
     */

    Heap(int size)
    {
        length = size;
        heap.reserve(length);
        count = 0;
    }

    /**
     *
     * Returns: heap size
     */
    int size()
    {
        return count;
    }

    /**
     * Tests if the heap is empty
     *
     * Returns: true is heap empty, false otherwise
     */
    bool empty()
    {
        return size()==0;
    }

    /**
     * Clears the heap.
     */
    void clear()
    {
        heap.clear();
        count = 0;
    }

    struct CompareT
    {
        bool operator()(const T& t_1, const T& t_2) const
        {
            return t_2 < t_1;
        }
    };

    /**
     * Insert a new element in the heap.
     *
     * We select the next empty leaf node, and then keep moving any larger
     * parents down until the right location is found to store this element.
     *
     * Params:
     *     value = the new element to be inserted in the heap
     */
    void insert(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;
    }



    /**
     * Returns the node of minimum value from the heap (top of the heap).
     *
     * Params:
     *     value = out parameter used to return the min element
     * Returns: false if heap empty
     */
    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. */
    }
};

}

#endif //OPENCV_FLANN_HEAP_H_
