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 array
The first 3 methods to rotate an array by d elements has been discussed in this post.
Method 4 (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 reverse of A.
- Reverse B to get ArBr, where Br is 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 :
C++
// C++ program for reversal algorithm // of array rotation #include <bits/stdc++.h> using namespace std; /*Function to reverse arr[] from index start to end*/void rvereseArray(int arr[], int start, int end) { while (start < end) { int temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; start++; end--; } } /* Function to left rotate arr[] of size n by d */void leftRotate(int arr[], int d, int n) { rvereseArray(arr, 0, d-1); rvereseArray(arr, d, n-1); rvereseArray(arr, 0, n-1); } // Function to print an array void printArray(int arr[], int size) { for (int i = 0; i < size; i++) cout << arr[i] << " "; } /* Driver program to test above functions */int main() { int arr[] = {1, 2, 3, 4, 5, 6, 7}; int n = sizeof(arr)/sizeof(arr[0]); int d = 2; // in case the rotating factor is // greater than array length d = d % n; // Function calling leftRotate(arr, d, n); printArray(arr, n); return 0; } |
C
// C/C++ program for reversal algorithm of array rotation #include<stdio.h> /*Utility function to print an array */void printArray(int arr[], int size); /* Utility function to reverse arr[] from start to end */void rvereseArray(int arr[], int start, int end); /* Function to left rotate arr[] of size n by d */void leftRotate(int arr[], int d, int n) { rvereseArray(arr, 0, d-1); rvereseArray(arr, d, n-1); rvereseArray(arr, 0, n-1); } /*UTILITY FUNCTIONS*//* function to print an array */void printArray(int arr[], int size) { int i; for (i = 0; i < size; i++) printf("%d ", arr[i]); } /*Function to reverse arr[] from index start to end*/void rvereseArray(int arr[], int start, int end) { int temp; while (start < end) { temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; start++; end--; } } /* Driver program to test above functions */int main() { int arr[] = {1, 2, 3, 4, 5, 6, 7}; int n = sizeof(arr)/sizeof(arr[0]); int d = 2; // in case the rotating factor is // greater than array length d = d % n; leftRotate(arr, d, n); printArray(arr, n); return 0; } |
Java
// Java program for reversal algorithm of array rotation import java.io.*; class LeftRotate { /* Function to left rotate arr[] of size n by d */ static void leftRotate(int arr[], int d) { int n = arr.length; rvereseArray(arr, 0, d-1); rvereseArray(arr, d, n-1); rvereseArray(arr, 0, n-1); } /*Function to reverse arr[] from index start to end*/ static void rvereseArray(int arr[], int start, int end) { int temp; while (start < end) { temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; start++; end--; } } /*UTILITY FUNCTIONS*/ /* function to print an array */ static void printArray(int arr[]) { for (int i = 0; i < arr.length; i++) System.out.print(arr[i] + " "); } /* Driver program to test above functions */ public static void main (String[] args) { int arr[] = {1, 2, 3, 4, 5, 6, 7}; int n = arr.length; int d = 2; // in case the rotating factor is // greater than array length d = d % n; leftRotate(arr, d); // Rotate array by d printArray(arr); } } /*This code is contributed by Devesh Agrawal*/ |
Python
# Python program for reversal algorithm of array rotation # Function to reverse arr[] from index start to end def rverseArray(arr, start, end): while (start < end): temp = arr[start] arr[start] = arr[end] arr[end] = temp start += 1 end = end-1 # Function to left rotate arr[] of size n by d def leftRotate(arr, d): n = len(arr) rverseArray(arr, 0, d-1) rverseArray(arr, d, n-1) rverseArray(arr, 0, n-1) # Function to print an array def printArray(arr): for i in range(0, len(arr)): print arr[i], # Driver function to test above functions arr = [1, 2, 3, 4, 5, 6, 7] n = len(arr) d = 2 # in case the rotating factor is # greater than array length d = d % n leftRotate(arr, d) # Rotate array by 2 printArray(arr) # This code is contributed by Devesh Agrawal |
C#
// C# program for reversal algorithm // of array rotation using System; class GFG { /* Function to left rotate arr[] of size n by d */ static void leftRotate(int []arr, int d) { int n = arr.Length; rvereseArray(arr, 0, d-1); rvereseArray(arr, d, n-1); rvereseArray(arr, 0, n-1); } /* Function to reverse arr[] from index start to end*/ static void rvereseArray(int []arr, int start, int end) { int temp; while (start < end) { temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; start++; end--; } } /*UTILITY FUNCTIONS*/ /* function to print an array */ static void printArray(int []arr) { for (int i = 0; i < arr.Length; i++) Console.Write(arr[i] + " "); } // Driver code public static void Main () { int []arr = {1, 2, 3, 4, 5, 6, 7}; int n = arr.Length; int d = 2; // in case the rotating factor is // greater than array length d = d % n; leftRotate(arr, 2); // Rotate array by 2 printArray(arr); } } // This code is contributed by Sam007 |
PHP
<?php // PHP program for reversal // algorithm of array rotation /* Function to left rotate arr of size n by d */function leftRotate(&$arr, $d, $n) { rvereseArray($arr, 0, $d - 1); rvereseArray($arr, $d, $n - 1); rvereseArray($arr, 0, $n - 1); } /*Function to reverse $arr from index start to end*/function rvereseArray(&$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; // in case the rotating factor is // greater than array length $d = ($d % $n); // Function calling leftRotate($arr, $d, $n); printArray($arr, $n); // This code is contributed // by ChitraNayal ?> |
Output :
3 4 5 6 7 1 2
Time Complexity : O(n)
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