Php Program to check if matrix is upper triangular

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.

PHP

<?php
// PHP Program to check upper
// triangular matrix.
$N = 4;

// Function to check matrix is
// in upper triangular form or
// not.
function isUpperTriangularMatrix($mat)
{
    global $N;
    for ($i = 1; $i < $N; $i++)
        for ($j = 0; $j < $i; $j++)
            if ($mat[$i][$j] != 0)
                return false;
    return true;
}

    // Driver Code
    $mat = array(array(1, 3, 5, 3),
                 array(0, 4, 6, 2) ,
                 array(0, 0, 2, 5),
                 array(0, 0, 0, 6));

    if (isUpperTriangularMatrix($mat))
        echo "Yes";
    else
        echo"No";

// This code is contributed by anuj_67.
?>

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.

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