堆排序算法的实现！！

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

#define parent(i) (i)/2
#define left(i) 2*(i)
#define right(i) 2*(i)+1

int size;

void heapify(int a[], int i)
{
	int l = left(i), r = right(i), largest;
	if(l<=size && a[l] > a[i])
		largest = l;
	else largest = i;
	if(r<=size && a[r] > a[largest])
		largest = r;
	if(largest != i)
	{
		int t = a[i];
		a[i] = a[largest];
		a[largest] = t;
		heapify(a, largest);
	}
}

void build_heap(int a[])
{
	int len = size;
	for(int i=len/2; i>=1; i--)
		heapify(a, i);
}

void heap_sort(int a[])
{
	build_heap(a);
	for(int i=size; i>=2; i--)
	{
		int t = a[1]; a[1] = a[i]; a[i] = t;
		size--;
		heapify(a, 1);
	}
}

int main()
{
	int a[20];
	printf("请输入数据个数：\n");
	scanf("%d", &size);
	int len = size;
	printf("请输入%d个你要排序的数：\n", size);
	for(int i=1; i<=size; i++)
		scanf("%d", &a[i]);
	heap_sort(a);
	for(int i=1; i<len; i++)
		printf("%d ", a[i]);
	printf("%d\n", a[len]);
	return 0;
}