Java Program to Reverse an Array by Using Recursion

Java Program to Reverse an Array by Using Recursion

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Prerequisite: Recursion in Java

In the previous article, we have discussed about Java Program to Find LCM by Using Recursion

In this program we are going to see how to reverse an Array by using Recursion by Java programming language.

Java Program to Reverse an Array by Using Recursion

Lets assume there is an array say A[ ] which has 5 elements {77, 82, 100, 17, 95}

So the reverse of A[] = {95, 17, 100, 82, 77}

Now let’s see different ways to reverse an Array by using Recursion.

Method-1: Java Program to Reverse an Array By Using Static Input and Recursion

Approach:

  • Declare and initiate an integer array ‘A[]’
  • Call a user defined method reverseArray() and pass the array ‘A[]’ with first index ‘0’ and last index ‘A.length-1’ of the array as parameter.
  • Inside the user defined method, check if the first index is less than the last index if true then swap the elements else call reverseArray() method recursively like reverseArray(a, i+1, j-1).
  • Now the value of the user defined method reverseArray() is stored in an integer array say ‘B[]’.
  • Print each elements in the array B[] using for each loop.

Program:

import java.util.*;
import java.io.*;
public class Main 
{
    public static void main(String[] args)
    {
        //declare and initialize an integer array A[]
        int A[] = {0,1,2,3,4,5,6,7,8};
        //calling the user defined method reverseArray()
        //and store the result value inside an integer array say ‘B[]’
        int B[] = reverseArray(A,0,A.length-1);
        //display the array after reversing elements.
        System.out.println("The elements in reverse array are");
        for(int i:B)
            System.out.print(i+" ");
    }
    
    static int[] reverseArray(int[] a,int i,int j)
    {
        //check if 1st index is less than last index
        if(i<j)
        {
            //swap elements a[i],a[j]
            int temp=a[i];
            a[i]=a[j];
            a[j]=temp;
            // reverse the array by calling the reverseArray() method recursively.
            reverseArray(a, i+1, j-1);
        }
        return a;
    }
}

Output:

The elements in reverse array are
8 7 6 5 4 3 2 1 0

Method-2: Java Program to Reverse an Array By Using User Input and Recursion

Approach:

  • Create a scanner class.
  • Declare an integer variable say ‘n’ and prompt the user to enter it’s value, which is the size of the array.
  • Declare an integer array say ‘A[]’
  • Prompt the user to enter the elements inside the array.
  • The elements inside the Array A[] are added in sequential index position using a for loop. Where the loop starts from i=0 to i<n and the loop is incremented by 1.
  • Call a user defined method reverseArray() and pass the array ‘A[]’ with first index ‘0’ and last index ‘A.length-1’ of the array as parameter.
  • Inside the user defined method, check if the first index is less than the last index if true then swap the elements else call reverseArray() method recursively like reverseArray(a, i+1, j-1).
  • Now the value of the user defined method reverseArray() is stored in an integer array say ‘B[]’.
  • Print each elements in the array B[] using for each loop.

Program:

import java.util.*;
import java.io.*;
public class Main 
{
    public static void main(String[] args)
    {
        //create a scanner class object
        Scanner s = new Scanner(System.in);
        System.out.println("Enter no. of elements you want in array:");
        //declare the size of the array
        int n = s.nextInt();
        // declare the array and initialize it with user input
        int A[] = new int[n];
        System.out.println("Enter all the elements:");
        //get all the elements sequentially
        for(int i = 0; i < n; i++)
            A[i] = s.nextInt();
        //calling the user defined method reverseArray()
        //and store the result value inside an integer array say ‘B[]’
        int B[] = reverseArray(A,0,A.length-1);
        //print reversed array elements by using for-each loop
        System.out.println("The elements in reverse array are");
        for(int i:B)
            System.out.print(i+" ");
    }
    
    static int[] reverseArray(int[] a,int i,int j)
    {
        //check if 1st index is less than last index
        if(i<j)
        {
            //swap elements a[i],a[j]
            int temp=a[i];
            a[i]=a[j];
            a[j]=temp;
            // reverse the array by calling the reverseArray() method recursively.
            reverseArray(a, i+1, j-1);
        }
        return a;
    }
}

Output:

Enter no. of elements you want in array:
7
Enter all the elements:
12
36
25
45
69
78
17
The elements in reverse array are
17 78 69 45 25 36 12

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