View Code of Problem 51

#include<iostream>
#include<string>
#include<vector>
using namespace std;
int main() {
	int n,sum=0;
	cin >> n;
	vector<vector<int>> arr(n);
	for (int i = 0; i < n; i++)
		arr[i].resize(n);
	for (int i = 0; i < n; i++)
		for (int j = 0; j < n; j++)
			cin >> arr[i][j];
	for (int i = 0; i < n; i++)
		for (int j = 0; j < i + 1; j++)
			sum += arr[i][j];
	cout << sum << endl;

}