PHP Program for Reversal algorithm for array rotation
Last Updated :
22 Jul, 2024
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Write a function rotate(arr[], d, n) that rotates arr[] of size n by d elements.
Example :
Input : arr[] = [1, 2, 3, 4, 5, 6, 7]
d = 2
Output : arr[] = [3, 4, 5, 6, 7, 1, 2]
Rotation of the above array by 2 will make an array
The Reversal Algorithm:
Algorithm :
rotate(arr[], d, n)
reverse(arr[], 1, d) ;
reverse(arr[], d + 1, n);
reverse(arr[], 1, n);
Let AB are the two parts of the input array where A = arr[0..d-1] and B = arr[d..n-1]. The idea of the algorithm is :
- Reverse A to get ArB, where Ar is the reverse of A.
- Reverse B to get ArBr, where Br is the reverse of B.
- Reverse all to get (ArBr) r = BA.
Example:
Let the array be arr[] = [1, 2, 3, 4, 5, 6, 7], d =2 and n = 7
A = [1, 2] and B = [3, 4, 5, 6, 7]
- Reverse A, we get ArB = [2, 1, 3, 4, 5, 6, 7]
- Reverse B, we get ArBr = [2, 1, 7, 6, 5, 4, 3]
- Reverse all, we get (ArBr)r = [3, 4, 5, 6, 7, 1, 2]
Below is the implementation of the above approach :
<?php
// PHP program for reversal
// algorithm of array rotation
/* Function to left rotate
arr of size n by d */
function leftRotate(&$arr, $d, $n)
{
if ($d == 0)
return;
// in case the rotating factor is
// greater than array length
$d = ($d % $n);
reverseArray($arr, 0, $d - 1);
reverseArray($arr, $d, $n - 1);
reverseArray($arr, 0, $n - 1);
}
/*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++;
$end--;
}
}
// Function to
// print an array
function printArray($arr, $size)
{
for ($i = 0; $i < $size; $i++)
print $arr[$i]." ";
}
// Driver code
$arr = array(1, 2, 3,
4, 5, 6, 7);
$n = sizeof($arr);
$d = 2;
// Function calling
leftRotate($arr, $d, $n);
printArray($arr, $n);
// This code is contributed
// by ChitraNayal
?>
Output
3 4 5 6 7 1 2
Complexity Analysis:
- Time Complexity : O(n), where n represents the size of the given array.
- Auxiliary Space: O(1), no extra space is required, so it is a constant.
Please refer complete article on Reversal algorithm for array rotation for more details!
