Home / Java / Loop / Recursion / Java Program to Find the Reverse of a Number

Java Program to Find the Reverse of a Number

in , ,
reverse of a number

Java program to find the reverse of a number has been shown here. For example, if a number is 12345 then the reverse of the number is 54321. The following section covers both of the iterative and recursive approaches to find the reverse of a number. The algorithm, pseudocode and time complexity of the program have been shown below.






1. Algorithm to find reverse of a number


1. Take a number n as input.

2. Initialize a variable to 0 say reverse = 0.

3. Perform r = n % 10.

4. Perform reverse = reverse * 10 + r.

5. Perform n = n / 10

6. If n = 0 stop the process and display reverse as output else go to step 3.




2. Pseudocode to find reverse of a number


Input : A number $n$

Output : The reverse of the number $n$

1. Procedure reverse($n$):

2. $reverse \leftarrow 0$

3. Repeat until $n != 0$

4. $reverse \leftarrow reverse * 10 + (n \mod 10)$

5. $n \leftarrow n / 10$

6. Return $reverse$

7. End Procedure





3. Time complexity to find reverse of a number


Time Complexity: O(log(n))

Where n is the input number.





4. Program & output to find reverse of a number




4.1. Java Program & output to find reverse of a number using iteration

Code has been copied
/********************************
	alphabetacoder.com
Java program to find the reverse
of a number using iteration
*********************************/

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        // declare instance of Scanner class
        Scanner sc = new Scanner(System.in);

        // declare variables
        int num, revnum = 0, r;

        // take input of the number
        System.out.print("Enter the number = ");
        num = sc.nextInt();

        //find the reverse
        while (num != 0) {
            // extract the unit digit
            r = num % 10;
            // store the reverse number.
            // provide appropriate positional value
            // of each digit in each iteration.
            revnum = revnum * 10 + r;
            //divide the number by 10
            num = num / 10;
        }

        // display result upto 3 decimal places
        System.out.println("Reverse of the number = " + revnum);
    }
}

Output

Enter the number = 12345

Reverse of the number = 54321





4.2. Java Program & output to find reverse of a number using recursion

Code has been copied
/********************************
	alphabetacoder.com
Java program to find the reverse
of a number using recursion
*********************************/

import java.util.Scanner;

class Main {
    // recursive function to reverse a number
    int reverse(int num, int rev) {
        if (num == 0)
            return rev;
        else
            return reverse(num / 10, (rev * 10 + num % 10));
    }

    public static void main(String[] args) {
        // declare instance of Scanner class
        Scanner sc = new Scanner(System.in);

        // declare an object
        Main obj = new Main();

        // declare variables
        int num;

        // take input of the number
        System.out.print("Enter the number = ");
        num = sc.nextInt();

        // find the reverse by calling function
        // The function has two parameters.
        // First one is the number and second one
        // is for storing the reverse of a number
        // display the result
        System.out.println("Reverse of the number = " + obj.reverse(num, 0));
    }
}

Output

Enter the number = 7085

Reverse of the number = 5807





Labels: , ,