View Code of Problem 51

#include<iostream>
#include<vector>
#include<algorithm>
#include<iomanip>
#include<string>
#include<cmath>

using namespace std;


int main()
{
	int n;
	cin >> n;

	vector<vector<int>> mat(n, vector<int>(n));

	int sum = 0;
	for (int i = 0; i < n; i++) {

		for (int j = 0; j < n; j++) {

			cin >> mat[i][j];

			if (j <= i)
				sum += mat[i][j];
		}
	}

	cout << sum;
}