利用中位数进行快速排序

#include <iostream>
#include <ctime>
#include <boost/timer/timer.hpp>
using namespace boost::timer;
using namespace std;

int partition(int *a,int low,int high)//快速排序分割
{
int key=a[high];
int p=low-1;
int tmp;
for(int i=low;i<high;++i){
if(a[i]<=key){
p++;
tmp=a[i];
a[i]=a[p];
a[p]=tmp;
}
}
tmp=a[p+1];
a[p+1]=key;
a[high]=tmp;

/*for(int i=low;i<=high;i++){
cout<<a[i]<<"\t";
}
cout<<endl;*/

return p+1;
}

int random_partition(int *a,int low,int high)//随机化快速排序
{
int rnd=rand()%(high-low+1)+low;//随机生成
int tmp=a[high];
a[high]=a[rnd];
a[rnd]=tmp;
return partition(a,low,high);
}

int random_select(int *a,int low,int high,int index)//找出第index个最小元素
{
if(low == high){
return a[low];
}
int p=random_partition(a,low,high);
/*for(int i=low;i<=high;i++){
cout<<a[i]<<"\t";
}
cout<<endl;*/
//int k=p;

//int p=partition(a,low,high);

if(p==index)
return a[p];
else if(p<index){
return random_select(a,p+1,high,index);
}else{
return random_select(a,low,p-1,index);
}
}

void best_case_quicksort(int *a,int low,int high)
{
if(low<high){
int index=((low+high)>>1);
random_select(a,low,high,index);//取中位数
//int q = partition(a,low,high);
best_case_quicksort(a,low,index-1);
best_case_quicksort(a,index+1,high);
}
}

void naive_quicksort(int *a,int low,int high)
{
if(low<high){
int q = partition(a,low,high);
naive_quicksort(a,low,q-1);
naive_quicksort(a,q+1,high);
}
}

int main()
{
srand((unsigned)time(NULL));
int count;
while (count=rand()%10,count<3);
count=10000000;
int *a=new int[count];
int *b=new int[count];
for(int i=0;i<count;++i){
a[i]=rand()%10000001-5000000;
b[i]=a[i];
//cout<<a[i]<<"\t";
}
cout<<endl;

cpu_timer t1;
t1.start();
naive_quicksort(a,0,count-1);
t1.stop();
cout<<t1.format();

////for(int i=0;i<count;i++){
////	cout<<a[i]<<"\t";
////}
////cout<<endl;

cpu_timer t2;
t2.start();
best_case_quicksort(b,0,count-1);
t2.stop();
/*for(int i=0;i<count;++i){
cout<<b[i]<<"\t";
}
cout<<endl;*/
cout<<t2.format();
delete[]a;
delete[]b;
}