Php Program for Reversal algorithm for right rotation of an array

Given an array, right rotate it by k elements. 

After K=3 rotation 

Examples:

Input: arr[] = {1, 2, 3, 4, 5, 
                6, 7, 8, 9, 10}
          k = 3
Output: 8 9 10 1 2 3 4 5 6 7

Input: arr[] = {121, 232, 33, 43 ,5}
           k = 2
Output: 43 5 121 232 33

Note : In the below solution, k is assumed to be smaller than or equal to n. We can easily modify the solutions to handle larger k values by doing k = k % n
Algorithm:

rotate(arr[], d, n)
  reverseArray(arr[], 0, n-1) ;
  reverse(arr[], 0, d-1);
  reverse(arr[], d, n-1);

Below is the implementation of above approach: 

PHP

<?php
// PHP program for right rotation of
// an array (Reversal Algorithm)

/*Function to reverse arr[]
from index start to end*/
function reverseArray(&$arr, $start, $end)
{
    while ($start < $end)
    {
        $temp = $arr[$start];
        $arr[$start] = $arr[$end];
        $arr[$end] = $temp;
        $start++;
        $end--;
    }
}

/* Function to right rotate arr[]
of size n by d */
function rightRotate(&$arr, $d, $n)
{
    reverseArray($arr, 0, $n - 1);
    reverseArray($arr, 0, $d - 1);
    reverseArray($arr, $d, $n - 1);
}

/* function to print an array */
function printArray(&$arr, $size)
{
    for ($i = 0; $i < $size; $i++)
        echo $arr[$i] . " ";
}

// Driver code
$arr = array(1, 2, 3, 4, 5,
             6, 7, 8, 9, 10);

$n = sizeof($arr);
$k = 3;

rightRotate($arr, $k, $n);
printArray($arr, $n);

// This code is contributed by ita_c
?>

Output:

8 9 10 1 2 3 4 5 6 7 

Time Complexity: O(N)

Auxiliary Space: O(1)

Please refer complete article on Reversal algorithm for right rotation of an array for more details!