堆排序

#define LeftChild(i)(2 * (i) + 1)

void PercDown(int a[], int i, int n)
{
    int c, t;
    for(t = a[i]; LeftChild(i) < n; i = c)
    {
        c = LeftChild(i);
        if(c != n - 1 && a[c + 1] > a[c])
            c++;
        if(t < a[c])
            a[i] = a[c];
        else
            break;
    }
    a[i] = t;
}

void Heapsort(int a[], int n)
{
    int i, t;
    i = n / 2 + 1;
    while(i--)
        PercDown(a, i, n);
    i = n;
    while(--i)
    {
        t = a[0];
        a[0] = a[i];
        a[i] = t;
        PercDown(a, 0, i);
    }
}