排序-堆排序

#include<iostream>
using namespace std;

void swap(int arr[], int i, int j)
{
    int temp = arr[i];
    arr[i] = arr[j];
    arr[j] = temp;
}

void heapify(int tree[], int n, int i)//n是结点总数，i是调整的结点数组下标
{
    //函数heapify对元素tree[i]进行调整
    if (i >= n)
    {
        return;        //递归出口
    }

    int c1 = 2 * i + 1;
    int c2 = 2 * i + 2;
    int max = i;
    if (c1<n&&tree[c1]>tree[max])
    {
        max = c1;
    }
    if (c2<n&&tree[c2]>tree[max])
    {
        max = c2;
    }
    if (max != i)
    {
        swap(tree, max, i);
        heapify(tree, n, max);    //对下面的结点继续调整
    }
}

void build_heap(int tree[], int n)    //建立大根堆
{
    int last_node = n - 1;
    int parent = (last_node - 1) / 2;    //找到最后一个非叶子结点
    int i;
    for (i = parent; i >= 0; i--)    //不断向上调整
    {
        heapify(tree, n, i);
    }
}

void heap_sort(int tree[], int n)    //堆排序
{
    build_heap(tree, n);
    int i;
    for (i = n - 1; i >= 0; i--)
    {
        swap(tree, i, 0);
        heapify(tree, i, 0);//由于每次都会减少一个最大值结点，故用i
    }
}
int main()
{
    int tree[] = { 4,10,2,5,1,3,8,7,1};
    int n = 9;
    //heapify(tree, n, 0);
    //build_heap(tree, n);
    heap_sort(tree, n);
    
    for (int i = 0; i < n; i++)
    {
        cout << tree[i] << endl;
    }

    system("pause");
}