算法导论习题7-4—快排中堆栈深度的优化

//Quick_sort
//timecomplexityisnlgn
//thewayisfindanelement,andpartitionthearrayaccordingtothiselement

#include<iostream>
usingnamespacestd;
intPartition(inta[],intp,intr)
{
	intnum=a[r];
	inti=p-1;
	intj,temp;
	//partitionthearrayaccordingtonum
	for(j=p;j<=r-1;j++)
	{
		if(a[j]<num)
		{
			i+=1;
			temp=a[j];
			a[j]=a[i];
			a[i]=temp;
		}
	}
	//Insertthenumbetweenthepartion
	temp=a[r];
	a[r]=a[i+1];
	a[i+1]=temp;
	//returnthepartitionboundray
	returni+1;
}
//RandomizedPartition,inthisfunctionwerandomselect
//theelementinarray,andexchangeitwiththelaseelementinarray
//thetargetislowdowntheaveragetimecomplexity!
intRandomizedPartition(inta[],intp,intr)
{
	//generateibetweenpandr
	inti=rand()%(r+1-p)+p;
	inttemp;
	temp=a[i];
	a[i]=a[r];
	a[r]=temp;
	returnPartition(a,p,r);
}
//recursivecallsQuickSorttocpmplatethesort
voidQuickSort(inta[],intp,intr)
{
	intq;
	if(p<r)
	{
		q=RandomizedPartition(a,p,r);
		QuickSort(a,p,q-1);
		QuickSort(a,q+1,r);
	}
}
//tailrecursiveQuickSort
//thedeapthoftheheapduetotherunofrecursiveQuickSortislgn
//直觉上每次partition如果都能对半划分，则递归的堆栈深度为lgn
//但是这种情况为理想状态，我们可以每次都挑出划分的子数组中较短的进行递归的QuickSort
//剩下的另一半用循环来处理。
voidTRQuickSort(inta[],intp,intr)
{
	intq;
	while(p<r)
	{
		q=RandomizedPartition(a,p,r);
		if((q-p)<(r-q))
		{
			TRQuickSort(a,p,q-1);
			p=q+1;
		}
		else
		{
			TRQuickSort(a,q+1,r);
			r=q-1;
		}
	}
}
intmain()
{
	intarr[10]={5,2,3,6,1,7,6,9,5,10};
	TRQuickSort(arr,0,9);
	inti;
	for(i=0;i<10;i++)
	{
		cout<<arr[i]<<"";
	}
	cout<<endl;
	return0;
}