[算法 笔记]大根堆

/**
 * 大根堆。从STL中获得。
 */

#include <iostream>
#include <ctime>
#include <cmath>
#include <cstdlib>

using namespace std;

void _push_heap(int *start, int holeIndex, int topIndex, int value)
{
    int parent = (holeIndex - 1) / 2;
    while (holeIndex > topIndex  && *(start + parent) < value)
    {
        *(start + holeIndex) = *(start + parent);
        holeIndex = parent;
        parent = (holeIndex - 1) / 2;
    }
    *(start + holeIndex) = value;
}

void adjust_heap(int *start, int holeIndex, int length, int value)
{
    int topIndex = holeIndex;
    int secondChild = 2 * holeIndex + 2;

    while (secondChild < length)
    {
        // 大根堆的调整
        if (*(start + secondChild) < *(start + secondChild - 1))
            secondChild--;
        *(start + holeIndex) = *(start + secondChild);
        holeIndex = secondChild;
        secondChild = 2 * holeIndex + 2;
    }

    if (secondChild == length) {
        *(start + holeIndex) = *(start + secondChild - 1);
        holeIndex = secondChild - 1;
    }

    _push_heap(start, holeIndex, topIndex, value);
}


void push_heap(int *start, int *end)
{
    _push_heap(start, start - end - 1, 0, *(end - 1));
}

int pop_heap(int *start, int *end)
{
    int result = *start;
    adjust_heap(start, 0, end - start, *(end - 1));

    return result;
}

void make_heap(int *start, int *end)
{
    if (end - start < 2) return ;
    int length = end - start;
    int parent = (length - 2) / 2;

    while (true) {
        adjust_heap(start, parent, length, *(start + parent));
        if (parent == 0) return;
        parent--;
    }
}

void sort_heap(int *start, int *end)
{
    while (end - start > 1)
        cout << pop_heap(start, end--) << "\t" ;
}

int test(void)
{
    enum {maxsize = 500};
    int a[maxsize], i;
    srand((int)time(0));

    cout << "test array: " << endl;
    for (i = 0; i < maxsize; i++)
    {
        a[i] = rand();
        cout << a[i] << "\t";
    }
    int size = sizeof(a) / sizeof(int);
    cout << endl << endl;
    cout << "result: " << endl;

    make_heap(a, a + size);
    sort_heap(a, a + size);

    return 0;
}

int main()
{
    test();

    return 0;
}