题解 | 上三角矩阵判定

#include<bits/stdc++.h>
using namespace std;
int main() {
    vector<vector<int>>nums;
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) {
        vector<int>row;
        for (int j = 0; j < n; j++) {
            int num;
            cin >> num;
            row.push_back(num);
        }
        nums.push_back(row);
    }
    bool is_open_triangular = true;
    for (int i = 0; i < n; i++) {

        for (int j = 0; j < i; j++) {
            if (nums[i][j] != 0) {
                is_open_triangular = false;
                i = n;
                j = n;
                break;
            }
        }
    }

    if (is_open_triangular) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }

    return 0;
}