중위값을 이용한 퀵정렬 개선에 대한 질문입니다.

#include<iostream>
 
using namespace std;
 
void swap(int& ref1,int& ref2){
     int temp=ref1;
     ref1=ref2;
     ref2=temp;
     return;
}
 
void median(int* arr,int left,int right){
     if(arr[left]>arr[(left+right)/2]){swap(arr[left],arr[(left+right)/2]);}
     if(arr[left]>arr[right]){swap(arr[left],arr[right]);}
     if(arr[(left+right)/2]>arr[right]){swap(arr[(left+right)/2],arr[right]);}
     swap(arr[left],arr[(left+right)/2]);
     return;
}
 
int partition(int* arr,int left,int right){
    median(arr,left,right);
    int first=left;
    int pivot=arr[first];
    left++;
    while(left<=right){
                      while(left<right&&arr[left]<=pivot){left++;}
                      while(left<=right&&arr[right]>=pivot){right--;}
                      if(left<right){swap(arr[left],arr[right]);}
                      else{break;}
    }
    swap(arr[first],arr[right]);
    return right;
}
 
void quick_sort(int* arr,int left,int right){
     if(left<right){
                    int index=partition(arr,left,right);
                    quick_sort(arr,left,index-1);
                    quick_sort(arr,index+1,right);
     }
     return;
}
 
int main(void){
    int N,*arr;
    cin>>N;
    arr=new int[N];
    for(int i=0;i<N;i++){cin>>arr[i];}
    quick_sort(arr,0,N-1);
    for(int i=0;i<N;i++){cout<<arr[i]<<" ";}
    delete []arr;
    system("PAUSE");
    return 0;
}