1.堆排序的实现：

如果要升序输出，则实现大堆
如果要降序输出，则实现小堆

逻辑：（升序输出）
将堆顶的元素和最后一个元素交换位置，此时左子树和右子树分别仍是大堆的顺序，交换位置后选出了最小的数。接着向下调整使剩余的元素再成为一个大堆，然后再交换，选出第二小的数…

代码：
Heap.h:

#include<stdio.h>
#include<assert.h>
#include<stdlib.h>
#include<time.h>
void Swap(int* p1, int* p2);
void AdjustDown(int* a, int n,int parent);
void AdjustUp(int* a, int child);
void HPSort(int* a, int n);

Heap.c:

#include<stdio.h>
#include<assert.h>
#include<stdlib.h>
#include"Heap.h"

void Swap(int* p1, int* p2)
{
	int tmp = *p1;
	*p1 = *p2;
	*p2 = tmp;
}
//向下调整：（建小堆）
void AdjustDown(int* a, int n,int parent)
{
	int child = 2 * parent + 1;
	while (child < n)
	{
		if (child + 1 < n && a[child + 1] > a[child])
		{
			child = child + 1;
		}
		if (a[parent] < a[child])
		{
			Swap(&a[parent], &a[child]);
			parent = child;
			child = 2 * child + 1;
		}
		else
			break;
	}
}
//向上调整：（建大堆）
void AdjustUp(int*a,int child)
{
	assert(a);	
	int parent = (child - 1) / 2;
	while (child != parent)
	{
		if (a[child] > a[parent])
		{
			Swap(&a[child], &a[parent]);
			child = parent;
			parent = (parent - 1) / 2;
		}
		else
			break;

	}

}

//堆排序（升序）：
void HPSort(int* a,int n)
{
	int end = n - 1;
	//建立大堆：
	for (int i = 1;i < n;i++)
	{
		AdjustUp(a, i);
	}
	while (end > 0)
	{
		Swap(&a[0], &a[end]);
		AdjustDown(a, end, 0);
		end--;
	}
}

2.TopK问题

将生成的一百万个随机数写入文件里面：
(Heap.h和Heap.c未改动）

#include"Heap.h"
//造数据：
void CreateData()
{
	int n = 1000000;
	srand(time(0));
	const char* file = "data.txt";
	FILE* fin = fopen(file, "w");
	if (fin == NULL)
	{
		perror("fopen error");
		return;
	}
	for (int i = 0;i < n;i++)
	{
		int x = (rand() + i) % 10000000;
		fprintf(fin, "%d\n", x);
	}
	fclose(fin);
}
//打印最大的k个数：
void PrintTopk(const char* file, int k)
{
	FILE* fout = fopen(file, "r");
	if (fout == NULL)
	{
		perror("fopen error");
		return;
	}
	int* minheap = (int*)malloc(sizeof(int) * k);
	int x = 0;
	for (int i = 0;i < k;i++)
	{
		fscanf(fout, "%d", &minheap[i]);
		AdjustUp(minheap, i);
	}
	while (fscanf(fout, "%d", &x) != EOF)
	{
		if (x > minheap[0])
		{
			minheap[0] = x;
			AdjustDown(minheap, k, 0);
		}
	}
	for (int i = 0;i < k;i++)
	{
		printf("%d ", minheap[i]);
	}
	printf("\n");
	free(minheap);
	fclose(fout);
}
int main()
{
	CreateData();
	PrintTopk("data.txt", 5);
	return 0;
}