题解 | #KiKi判断上三角矩阵#

#include <stdio.h>

int main() {
    int num = 0;
    while (scanf("%d", &num) != EOF) 
    { 
        int arr[10][10] = {0};
        for (int i = 0; i <num;i++)
        {
            for (int j = 0; j < num; j++)
            {
                scanf("%d",arr[i] + j);
            }
        }

        int flag = 0;
        for (int i = 1; i < num; i++)
        {
            for (int j = 0; j < i; j++)
            {
                if (arr[i][j] != 0)
                {
                    flag++;
                }
            }
        }
        if (flag)
        {
            printf("NO");
        }
        else
        {
            printf("YES");
        }
    }
    return 0;
}