归并之后别忘记取模啊

int ans = 0;
//[l,r)
void merge_sort(vector<int>&A, int l, int r, int *T)
{
    if(r-l >1)
    {
        int mid = l+(r-l)/2;
        int ll = l, rr = mid,i = l;
        merge_sort(A, l, mid, T);
        merge_sort(A, mid, r, T);
        while(ll<mid || rr < r)
        {
            if(rr>=r || (ll<mid && A[ll]<=A[rr]))
                T[i++]=(A[ll++]);
            else {
                T[i++]=(A[rr++]);
                ans += mid - ll;
            }
        }
        for(int i = l;i < r;i ++)
            A[i] = T[i];
    }
    return;
}
int InversePairs(vector<int> data) {
    int * tmp = new int[data.size() + 10];
    merge_sort(data, 0, data.size(),tmp);
    return ans;
}