Given a square matrix and the task is to check the matrix is in upper triangular form or not. A square matrix is called upper triangular if all the entries below the main diagonal are zero.
 

Examples: 
 

Input : mat[4][4] = {{1, 3, 5, 3},
                     {0, 4, 6, 2},
                     {0, 0, 2, 5},
                     {0, 0, 0, 6}};
Output : Matrix is in Upper Triangular form.

Input : mat[4][4] = {{5, 6, 3, 6},
                     {0, 4, 6, 6},
                     {1, 0, 8, 5},
                     {0, 1, 0, 6}};
Output : Matrix is not in Upper Triangular form.

# Python3 Program to check upper 
# triangular matrix.

# Function to check matrix 
# is in upper triangular
def isuppertriangular(M):
    for i in range(1, len(M)):
        for j in range(0, i):
            if(M[i][j] != 0): 
                    return False
    return True
    
# Driver function.
M = [[1,3,5,3],
    [0,4,6,2],
    [0,0,2,5],
    [0,0,0,6]]

if isuppertriangular(M):
    print ("Yes")
else:
    print ("No")

# This code is contributed by Anurag Rawat

Output: 
 

Yes

Time Complexity: O(n²), where n represents the number of rows and columns of the matrix.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

Please refer complete article on Program to check if matrix is upper triangular for more details!