题解 | 上三角矩阵判定

#include <iostream>
#include <vector>
using namespace std;

int main() {
    int n;
    cin >> n;
    int arr[n][n];
    bool a = true;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> arr[i][j];
            }
        }
    for (int i = 1; i < n; i++) {
        for (int j = 0; j < i; j++) {
            cin >> arr[i][j];
            if (arr[i][j] != 0) {
                a = false;
                break;
            }
        }
        if (!a) {
            break;
        }
    }
    if (a) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
}