POJ2299+逆序数

归并排序！！！！！！！！！！

 /*
 归并排序+求逆序数
 */
 #include<stdio.h>
 #include<string.h>
 #include<algorithm>
 #include<stdlib.h>
 using namespace std;
 typedef __int64 int64;
 const int maxn = ;
 int64 a[ maxn ],Sort[ maxn ];
 int64 res;
 
 void init(){
     res = ;
 }
 
 void merge( int L,int R ){
     int mid = (L+R)/;
     int i = L;
     int j = mid+;
     int pos = L;
     while( i<=mid&&j<=R ){
         if( a[i]<a[j] )
             Sort[ pos++ ] = a[i++];
         else{
             Sort[ pos++ ] = a[j++];
             res += (mid-i+);
         }
     }
     while( i<=mid )
         Sort[ pos++ ] = a[i++];
     while( j<=R )
         Sort[ pos++ ] =  a[j++];
     for( int k=L;k<=R;k++ )
         a[k] = Sort[k];
 }
 
 void merge_sort( int L,int R ){
     int mid = (L+R)/;
     if( L<R ){
         merge_sort( L,mid );
         merge_sort( mid+,R );
         merge( L,R );
     }
     return ;
 }
 
 int main(){
     int n;
     while( scanf("%d",&n),n ){
         for( int i=;i<=n;i++ )
             scanf("%I64d",&a[i]);
         init();
         merge_sort( ,n );
         printf("%I64d\n",res);
     }
     return ;
 }