ZZULIOJ 1125: 上三角矩阵的判断，Java

import java.util.Scanner;
public class Main {
    static Scanner cin = new Scanner(System.in);
    static int [][]a = new int[21][21];
    public static void main(String[] args) {
        int n=cin.nextInt();
        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++)
                a[i][j]=cin.nextInt();

            int flag=0;
            for(int i=1;i<=n;i++)
                for(int j=1;j