def is_upper_triangular(matrix): n = len(matrix) for i in range(n): for j in range(i): if matrix[i][j] != 0: return "NO" return "YES" n = int(input()) matrix = [list(map(int, input().split())) for _ in range(n)] print(is_upper_triangular(matrix))
def is_upper_triangular(matrix): n = len(matrix) for i in range(n): for j in range(i): if matrix[i][j] != 0: return "NO" return "YES" n = int(input()) matrix = [list(map(int, input().split())) for _ in range(n)] print(is_upper_triangular(matrix))