题解 | 上三角矩阵判定-Java

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[][] matrix = new int[n][n];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                matrix[i][j] = in.nextInt();
            }
        }

        boolean flag = true;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < i; j++) {
                if (matrix[i][j] != 0) {
                    flag = false;
                }
            }
        }

        if (flag) System.out.println("YES");
        else System.out.println("NO");
    }
}