归并排序求逆序数;

#include 
     
      #define MAXN 5000+10#define LL long long#include 
      
       using namespace std;int a[MAXN], tmp[MAXN]; int b[MAXN];LL ans;void Merge(int l, int m, int r){    int i=l;    int j=m+1;    int k=l;    while(i<=m && j<=r)    {        if(a[i]> a[j])        {            tmp[k++]=a[j++];            ans+=m-i+1;        }        else        {            tmp[k++]=a[i++];        }    }    while(i<=m) tmp[k++]=a[i++];    while(j<=r) tmp[k++]=a[j++];    for(int i=l; i<=r; i++)    {        a[i]=tmp[i];    }}void Merge_sort(int l, int r){    if(l 
       
        > 1;        Merge_sort(l, m);        Merge_sort(m+1, r);        Merge(l, m, r);    }}int main(){    int n; LL res;    while(scanf("%d", &n) != EOF)    {        for(int i=0; i