堆排序例子

#include <stdio.h>

void exch(int& a, int &b)
{
    int tmp = a;
    a = b;
    b = tmp;
}


void fixdown(int a[], int k, int N)
{
    while(2*k <= N)
    {
        int j=k*2;
        if(j<N && a[j]<a[j+1]) j++;
        if(!(a[k]<a[j])) break;
        exch(a[k], a[j]);
        k = j;
    }
}

void heapsort(int a[], int l, int r)
{
    int k, N=r-l+1;
    int *pq = a+l-1; //notice!
    for(k = N/2; k>=1; k--)
        fixdown(pq, k, N);
    while(N>1)
    {
        exch(pq[1], pq[N]);
        fixdown(pq, 1, --N);
    }
}

int main()
{
    int a[10] = {3,5,4,8,6,9,6,5,4,1};
    heapsort(a, 0, 9);
    for(int i=0; i<10; i++)
        printf("%d ", a[i]);
    printf("\n");
    return 0;
}