Php Program to Interchange elements of first and last rows in matrix

Given a 4 x 4 matrix, we have to interchange the elements of first and last row and show the resulting matrix.
Examples :

Input : 3 4 5 0
        2 6 1 2
        2 7 1 2
        2 1 1 2
Output : 2 1 1 2
         2 6 1 2
         2 7 1 2
         3 4 5 0

Input : 9 7 5 1
        2 3 4 1
        5 6 6 5
        1 2 3 1
Output : 1 2 3 1
         2 3 4 1
         5 6 6 5
         9 7 5 1

The approach is very simple, we can simply swap the elements of first and last row of the matrix inorder to get the desired matrix as output.
Below is the implementation of the approach : 

PHP

<?php
// PHP code to swap the element of first
// and last row and display the result
$n = 4;

function interchangeFirstLast(&$m)
{
        global $n;
        $rows = $n;

        // swapping of element between first
        // and last rows
        for ($i = 0; $i < $n; $i++)
        {
            $t = $m[0][$i];
            $m[0][$i] = $m[$rows - 1][$i];
            $m[$rows - 1][$i] = $t;
        }
}

// Driver function

// input in the array
$m = array(array(8, 9, 7, 6),
            array(4, 7, 6, 5),
            array( 3, 2, 1, 8),
            array(9, 9, 7, 7));

interchangeFirstLast($m);

// printing the interchanged matrix
for ($i = 0; $i < $n; $i++)
{
    for ($j = 0; $j < $n; $j++)
        echo $m[$i][$j] . " ";
    echo "
";
}
?>

Output :

9 9 7 7 
4 7 6 5 
3 2 1 8 
8 9 7 6 

Time Complexity: O(N) where N is no of rows; as we are using single loop for interchanging first and last rows of a given matrix.

Auxiliary Space: O(1), as we are not using any extra space.

Please refer complete article on Interchange elements of first and last rows in matrix for more details!