12918 - Lucky Thief

程式碼:

#include <iostream>
using namespace std;


int main()
{
    int t,n,m;
    cin>>t;
    while(t--)
    {
        cin>>n>>m;
        long long int up=m-1,down=m-n;
        
        cout<<(up+down)*n/2<<endl;
    }
    return 0;
}