PHP Program for Reversal algorithm for array rotation (original) (raw)
Last Updated : 23 Jul, 2025
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 `
d,d, d,n) { if ($d == 0) return; // in case the rotating factor is // greater than array length d=(d = (d=(d % $n); reverseArray($arr, 0, $d - 1); reverseArray($arr, d,d, d,n - 1); reverseArray($arr, 0, $n - 1); } /*Function to reverse $arr from index start to end*/ function reverseArray(&$arr, start,start, start,end) { while ($start < $end) { temp=temp = temp=arr[$start]; arr[arr[arr[start] = arr[arr[arr[end]; arr[arr[arr[end] = $temp; $start++; $end--; } } // Function to // print an array function printArray($arr, $size) { for ($i = 0; i<i < i<size; $i++) print arr[arr[arr[i]." "; } // Driver code $arr = array(1, 2, 3, 4, 5, 6, 7); n=sizeof(n = sizeof(n=sizeof(arr); $d = 2; // Function calling leftRotate($arr, d,d, d,n); printArray($arr, $n); // This code is contributed // by ChitraNayal ?>`
**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!