Java Program to Rotate an Array

Introduction

Rotating an array involves shifting the elements of the array either to the left or the right by a specified number of positions. This task is common in various algorithms and applications, such as circular buffers or scheduling tasks. This guide will walk you through writing a Java program that rotates an array to the right by a specified number of positions.

Problem Statement

Create a Java program that:

• Prompts the user to enter the size of an array and its elements.
• Prompts the user to enter the number of positions by which the array should be rotated.
• Rotates the array to the right by the specified number of positions.
• Displays the rotated array.

Example:

• Input:
  • Array: [1, 2, 3, 4, 5]
  • Rotate by: 2
• Output: "Rotated array: [4, 5, 1, 2, 3]"

Solution Steps

1. Read the Array Size, Elements, and Rotation Count: Use the Scanner class to take the size, elements, and the number of positions to rotate as input from the user.
2. Rotate the Array: Implement the logic to rotate the array to the right by the specified number of positions.
3. Display the Rotated Array: Print the rotated array.

Java Program

// Java Program to Rotate an Array // Author: https://www.rameshfadatare.com/ import java.util.Scanner; public class RotateArray { public static void main(String[] args) { // Step 1: Read the size, elements of the array, and rotation count from the user Scanner scanner = new Scanner(System.in); System.out.print("Enter the size of the array: "); int size = scanner.nextInt(); int[] array = new int[size]; System.out.println("Enter the elements of the array:"); for (int i = 0; i < size; i++) { array[i] = scanner.nextInt(); } System.out.print("Enter the number of positions to rotate the array: "); int k = scanner.nextInt(); // Step 2: Rotate the array rotateArray(array, k); // Step 3: Display the rotated array System.out.println("Rotated array:"); for (int i = 0; i < array.length; i++) { System.out.print(array[i] + " "); } } // Method to rotate the array to the right by k positions public static void rotateArray(int[] array, int k) { int n = array.length; k = k % n; // In case k is greater than the length of the array // Step 2.1: Reverse the whole array reverseArray(array, 0, n - 1); // Step 2.2: Reverse the first k elements reverseArray(array, 0, k - 1); // Step 2.3: Reverse the remaining elements reverseArray(array, k, n - 1); } // Method to reverse a portion of the array public static void reverseArray(int[] array, int start, int end) { while (start < end) { int temp = array[start]; array[start] = array[end]; array[end] = temp; start++; end--; } } } 

Explanation

Step 1: Read the Array Size, Elements, and Rotation Count

• The Scanner class is used to read the size of the array, the elements of the array, and the number of positions to rotate the array. The nextInt() method captures the size, elements, and rotation count.

Step 2: Rotate the Array

• The rotateArray() method rotates the array by k positions to the right:
  1. Calculate Effective Rotations: The number of positions k is adjusted using k = k % n to handle cases where k is greater than the length of the array.
  2. Reverse the Whole Array: The entire array is reversed using the reverseArray() method.
  3. Reverse the First k Elements: The first k elements of the reversed array are reversed again to restore their original order.
  4. Reverse the Remaining Elements: The remaining elements after the first k are reversed to restore their order.

Step 3: Display the Rotated Array

• The program prints the rotated array using a for loop.

Helper Method: Reverse the Array

• The reverseArray() method reverses a specified portion of the array by swapping elements from the start and end until they meet in the middle.

Output Example

Example 1:

Enter the size of the array: 5 Enter the elements of the array: 1 2 3 4 5 Enter the number of positions to rotate the array: 2 Rotated array: 4 5 1 2 3 

Example 2:

Enter the size of the array: 6 Enter the elements of the array: 10 20 30 40 50 60 Enter the number of positions to rotate the array: 3 Rotated array: 40 50 60 10 20 30 

Example 3:

Enter the size of the array: 4 Enter the elements of the array: 1 2 3 4 Enter the number of positions to rotate the array: 1 Rotated array: 4 1 2 3 

Conclusion

This Java program demonstrates how to rotate an array to the right by a specified number of positions. The program covers essential concepts such as array manipulation, reversing portions of an array, and handling rotations efficiently. This exercise is valuable for understanding in-place array operations and manipulating data structures in Java programming.