Codeforces Round ＃802 (Div. 2) 纯补题

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Codeforces Round #802 Div. 2
这次没打比赛，纯补题

A Optimal Path

简单题，甚至可以用循环，但我怕爆时间，简单推个公式

#include<bits/stdc++.h>

using namespace std;

#define int long long

const int N = 1e4 + 10;

int n, m;
int T;

signed main()
{
    
	cin>>T;
	while(T -- ){
    
		cin >> n >> m;
		int op = 0;
		if(m % 2) op += (m + 1) / 2 + m / 2 * (m + 1);
		else op += (m + 1) * m / 2;
		
		op -= m;
		for(int i = 1; i <= n; i ++ ){
    
			op += i * m;
		}
		cout<<op<<endl;
	}
	return 0;
}