题解 | #KiKi判断上三角矩阵#

#include <iostream>
using namespace std;

int main() {
    int a[10][10], c;
    cin >> c;
    for (int i = 0; i < c; i++) {
        for (int j = 0; j < c; j++) {
            cin >> a[i][j];
        }
    }
    for (int i = 0; i < c; i++) {
        for (int j = i - 1; j >= 0; j--) {
            if (i == c - 1 && j == 0 && a[i][j] == 0)
                cout << "YES";
            else if (a[i][j] != 0)
            {
                cout << "NO";
                return 0;
            }
        }
    }
}