Java Program for Reversal algorithm for array rotation
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
Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.
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 Java implementation of the above approach:
// Java program for reversal algorithm of array rotationimport 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 }; leftRotate(arr, 2); // Rotate array by 2 printArray(arr); }}/*This code is contributed by Devesh Agrawal*/ |
Output:
3 4 5 6 7 1 2
Time Complexity: O(n), where n is 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!
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