题解 | 上三角矩阵判定

import java.util.*;
public class Main{
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[][] p = new int[15][15];
        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++)p[i][j] = in.nextInt();
        for(int i=1;i<=n;i++){
            for(int j=1;j<=i-1;j++){
                if(p[i][j]!=0){
                    System.out.println("NO");
                    return;
                }
            }
        }
        System.out.println("YES");
    }
}