1.快速排序，0,1,2..n-1,   選出樞紐元index，交換a[index]與a[n-1]，將小於a[n-1]的元素放在左邊，大於的元素放在右邊，遞迴分別對兩組進行排序

#include<iostream>
using namespace std;
#include<time.h>

int RandomInRange(int left,int right)
{
	if(right>left)
	{
		srand(time(NULL));
		return left+rand()%(right-left);//產生start~end之間的隨機數
	}
}

int partion(int *a,int left,int right)
{
	if(a==NULL ||  left<0  ||  right<left)
	       throw new exception("invalid parameters");
	int index = RandomInRange(left,right);
	swap(a[index],a[right]);

	int i=left-1;
	for(int j=left;j<right;j++)
	{
		if(a[j]<a[right])
		{
			i++;
		    if(i!=j)
				swap(a[i],a[j]);
		}
	}

	++i;
	swap(a[i],a[right]);

	return i;
}

void quickSort(int *a,int left,int right)
{
	if(left == right)
		return ;
	int index= partion(a,left,right);
	if(index>left)
		quickSort(a,left,index-1);
	if(index<right)
		quickSort(a,index+1,right);
}

int main()
{
	int a[]={2,8,7,1,3,5,6,4};
	int length=sizeof(a)/sizeof(int);
	quickSort(a,0,length-1);
	for(int i=0;i<length;i++)
		cout<<a[i]<<"  ";
}