堆排序

堆排序

堆排序思想说起来还不太好组织语言。

它的做法就是，首先将待排序序列组织成一个大（小）顶堆，然后逐次将首元素和最后一个元素交换，序列长度减一后再次调整序列成一个大顶堆。自此就成了一个升（降）序列。

c代码如下：（参考《大话数据结构》）

void HeapAdjust (int * const piSrc, const int startIndex, const int len)
{
int parentIndex = startIndex;
int maxChildIndex;
int temp;
if (parentIndex < len)
{
temp = piSrc[parentIndex];
while ((parentIndex<len) && (2*parentIndex+1<len))
{
maxChildIndex = 2*parentIndex + 1; // left
if (maxChildIndex+1<len&&piSrc[maxChildIndex+1]>piSrc[maxChildIndex])
maxChildIndex ++; // right child is the max value
if (piSrc[maxChildIndex] > piSrc[parentIndex]) // if child value is greater than parent
piSrc[parentIndex] = piSrc[maxChildIndex]; // parent value = child value
else
break;
parentIndex = maxChildIndex;
piSrc[parentIndex] = temp;
}
}
}

void HeapSort (int * const piSrc, const int len)
{
int i;
int temp;
if (NULL != piSrc)
{
for (i=len/2-1; i>=0; i--)
HeapAdjust (piSrc, i, len);

for (i=len-1; i>0; i--)
{
temp = piSrc[i];
piSrc[i] = piSrc[0];
piSrc[0] = temp;
HeapAdjust (piSrc, 0, i);
}
}
}

注：
首先将序列调整成一个大顶堆，即每个结点数值都大于或等于左右孩子结点数值。

for (i=len/2-1; i>=0; i--)
HeapAdjust (piSrc, i, len);有左右孩子的结点最大索引即是len/2-1。

在HeapAdjust函数中，以startIndex为开始，逐次向下调整成大顶堆。即：如果左右孩子中最大的值比双亲节点的数值大，交换位置；否则，退出。

完整c代码如下：

#include <stdio.h>
#include <stdlib.h>

#include<windows.h>

void HeapAdjust (int * const piSrc, const int startIndex, const int len)
{
int parentIndex = startIndex;
int maxChildIndex;
int temp;
if (parentIndex < len)
{
temp = piSrc[parentIndex];
while ((parentIndex<len) && (2*parentIndex+1<len))
{
maxChildIndex = 2*parentIndex + 1; // left
if (maxChildIndex+1<len&&piSrc[maxChildIndex+1]>piSrc[maxChildIndex])
maxChildIndex ++; // right child is the max value
if (piSrc[maxChildIndex] > piSrc[parentIndex]) // if child value is greater than parent
piSrc[parentIndex] = piSrc[maxChildIndex]; // parent value = child value
else
break;
parentIndex = maxChildIndex;
piSrc[parentIndex] = temp;
}
}
}

void HeapSort (int * const piSrc, const int len)
{
int i;
int temp;
if (NULL != piSrc)
{
for (i=len/2-1; i>=0; i--)
HeapAdjust (piSrc, i, len);

for (i=len-1; i>0; i--)
{
temp = piSrc[i];
piSrc[i] = piSrc[0];
piSrc[0] = temp;
HeapAdjust (piSrc, 0, i);
}
}
}

int testArray[] = {1,3,5,7,9,2,4,6,8,0, 54, 48, 2 , 5 , 8};//{5,5,5,5,5,5,5,5,5,5,5};//

void PrintfIntArray (int * const pia, const int n)
{
int i;
for (i=0; i<n; i++)
printf("%u ", pia[i]);
printf("\n");
}

int main()
{
DWORD startTime;
DWORD endTime;
printf("Hello world!\n");

startTime = GetTickCount ();
HeapSort (testArray, sizeof(testArray)/sizeof(int));
endTime = GetTickCount();
printf ("Sort Time Consumption:%lu ms.\n", endTime-startTime);
PrintfIntArray (testArray, sizeof(testArray)/sizeof(int));

return 0;
}