排序算法（5）--快速排序QuickSort（非递归实现）

非递归写法

利用栈
主要需要记录起始和结尾即low和high 的值，用循环只能处理一边，所以需要将temp后面的起始和结尾下标记录下来。利用栈来记录（也可以使用队列）。

先将下标进栈:0,3,5,7;
先判断栈为不为空，不空说明还有未处理完的数对;
代码：
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <math.h>

int Partition(int *arr, int low, int high)
{
	int temp = arr[low];
	while(low < high)
	{
		while((low < high)&&(arr[high] >= temp))
		{
			high--;
		}
		if(low  == high)
		{
			break;
		}
		else
		{
			arr[low] = arr[high];
		}

		while((low < high)&&(arr[low] <= temp))
		{
			low++;
		}
		if(low == high)
		{
			break;
		}
		else
		{
			arr[high] = arr[low];
		}
	}

	arr[low] = temp;
	return low;
}

void QuickSort(int *arr, int len)
{
	int tmp = (int)ceil((log((double)len)/log((double)2)));//ceil向上取整,返回值为double类型
	//int *stack = (int *)malloc(sizeof(int)*2*(int)(log((double)len)/log((double)2)));//未向上取整
	int *stack = (int *)malloc(sizeof(int)*2*tmp);
	assert(stack != NULL);
	int top = 0;//栈顶指针，下标可取

	int low = 0;
	int high = len-1;
	int par = Partition(arr,low,high);
	if(par > low+1)//保证左边至少有两个数字
	{
		stack[top++] = low;//保存起始
		stack[top++] = par-1;//保存结尾
	}
	if(par < high-1)//保证右边至少有两个数字
	{
		stack[top++] = par+1;
		stack[top++] = high;
	}

	while(top > 0)
	{
		high = stack[--top];
		low = stack[--top];

		par = Partition(arr,low,high);

		if(par > low+1)//保证左边至少有两个数字
	{
		stack[top++] = low;//保存起始
		stack[top++] = par-1;//保存结尾
	}
	if(par < high-1)
	{
		stack[top++] = par+1;
		stack[top++] = high;
	}
	}

	free(stack);
}

void Show(int *arr,int len)
{
	for(int i=0; i<len; i++)
	{
		printf("%d ",arr[i]);
	}
	printf("\n");
}

int main()
{
	int arr[] = {32,2334,35,56,68,856,34,33};

	QuickSort(arr,sizeof(arr)/sizeof(arr[0]));
	Show(arr,sizeof(arr)/sizeof(arr[0]));
	return 0;
}