How to Switch the First Element of an Arrays Sub Array in PHP?

Given a 2D array where each element is an array itself, your task is to switch the first element of each sub-array with the first element of the last sub-array using PHP.

Example:

Input:  num = [
 ['a', 'b', 'c'],
 ['d', 'e', 'f'],
 ['g', 'h', 'i']
];

Output:  [
 ['g', 'b', 'c'],
 ['d', 'e', 'f'],
 ['a', 'h', 'i']
]

Using a Temporary Variable

In this approach, we store the first element of the first sub-array in a temporary variable and then replace the first element of the first sub-array with the first element of the last sub-array and at last assign the value stored in the temporary variable to the first element of the last sub-array.

Example: Below is the implementation of the above approach to switch the first element of each sub-array in a multidimensional array.

Array
(
 [0] => Array
 (
 [0] => g
 [1] => b
 [2] => c
 )

 [1] => Array
 (
 [0] => d
 [1] => e
 [2] => f
 ...

Time Complexity: O(1)

Auxiliary Space: O(1)