ZOJ 2386 今天最后一道题了，晚上要比赛，用了某大神的模板。加了个计数

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define N 500000

int a[N],b[N];
long long count;
void mergearray(int a[], int first, int mid, int last, int temp[])  
{  
    int i = first, j = mid + 1;  
    int m = mid,   n = last;  
    int k = 0;  
      
    while (i <= m && j <= n)  
    {  
        if (a[i] < a[j])  
            temp[k++] = a[i++];  
        else
        {  
            temp[k++] = a[j++];  
           count += (m-i+1);//记录交换的次数
         }   
    }  
      
    while (i <= m)  
        temp[k++] = a[i++];       
    while (j <= n)  
        temp[k++] = a[j++];        
    for (i = 0; i < k; i++)  
        a[first + i] = temp[i];  
}  

void mergesort(int a[], int first, int last, int temp[])  
{  
    if (first < last)  
    {  
        int mid = (first + last) / 2;  
        mergesort(a, first, mid, temp);      
        mergesort(a, mid + 1, last, temp);
        mergearray(a, first, mid, last, temp); 
    }  
}  
  
int main()
{
    int i,j,ncases,temp;
    
    while(scanf("%d",&ncases) && ncases)
    {
       for(i=0; i<ncases; i++)
         scanf("%d",&a[i]);
        count = 0;
       mergesort(a,0,ncases-1,b);       
        printf("%lld\n",count);
    } 
    return 0;
}