代码：
void HeapSort(int a[], int n){
int Tmp;
for (int i = n / 2; i >= 0; i--)
PercDown(a, i, n);
/*build a heap; we should know that intinially we put all of the elements randomly, then
we begin to percolate down the heap from the last element (n/2) which has the child;
notice that the elements we should percolate are always all the elements.*/
/*before the beginning of the formal heapsort, the array has been adjusted to a heap*/
for (int i = n - 1; i >= 1; i++){
Tmp = a[i];
a[i] = a[0];
a[0] = Tmp;
/*This step aim at remove the minimum element out of the heap,it‘s important to
understand the following progress of percolating the heap would not affect this
element*/
PercDown(a, 0, i);
/*We just percolate down the first elements, which would not affect those elements which
have been sorted*/
}
}
//下滤算法，从i节点开始调整，n为节点总数，从0开始计算，i节点的子节点为2*i+1,2*i+2
void PercDown(int a[], int i, int n)
{
int child, temp;
temp = a[i];/*remember the element which are expected to adjust*/
child = 2 * i + 1;
while (child < n){
if (child + 1 < n && a[child + 1] < a[child])
child++;
/*find the smaller child to ensure all two childs are all larger than the parent*/
if (a[child] >= temp) break;
/*if so, the position would be identified.*/
else{
a[i] = a[child];//make the smaller child become the parent node
i = child;//the child position become the new parent position
child = 2 * i + 1;// the new left child position
}
}
a[i] = temp;
/*find the appropriate position*/
}