这道题如果直接遍历查找的话肯定会超时，所以要用归并排序去写，其实也就是归并排序的模板，只是多了一行代码。还有就是需要开long long


AC代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <algorithm>
#define ll long long
using namespace std;
ll t[1000005];
ll a[1000005];
int T,n;
ll ans;
 
void merge(int left,int mid,int right){
  int i = left, j = mid + 1, k = left;
  while(i <= mid && j <= right){
    if(a[i] <= a[j]){
      t[k++] = a[i++];
    }
    else{
      ans += j - k;
      t[k++] = a[j++];
    }
  }
  while(i <= mid){
    t[k++] = a[i++];
  }
  while(j <= right){
    t[k++] = a[j++];
  }
  for(int i=left;i<=right;i++){
    a[i] = t[i];
  }
}
 
void mergesort(int left,int right){
  if(left < right){
    int mid = (left + right) / 2;
    mergesort(left,mid);
    mergesort(mid+1,right);
    merge(left,mid,right);
  }
}
 
int main()
{
  scanf("%d",&T);
  while(T--){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
      scanf("%d",&a[i]);
    }
    ans = 0;
    mergesort(1,n);
    printf("%lld\n",ans);
  }
  return 0;
}