Reverse a number in java – Java Program to Reverse a Number using Recursion

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Reverse a number in java: Beginners and experienced programmers can rely on these Best Java Programs Examples and code various basic and complex logics in the Java programming language with ease.

Java Program to Reverse a Number using Recursion

  • Write a Java program to reverse a number using recursion

To reverse a number we have to reverse the the sequence of digits in a number. After reversing, least significant digit(right most digit) will become most significant digit() of number and most significant digit becomes least significant digit and so on.

For Example

Befor reverse : 745362
After reverse : 263547
Here, we will reverse the digits of of a number using reversion using below mentioned recursive equation.

getReversedNumber(N) = lastDigitOf(N) x power(10, numberOfDigits(N/10))
                         + getReversedNumber(N/10)

Gere is the detailed explanation of above algorithm.
Algorithm to reverse a number using recursion

  • lastDigitOf(N) : This function returns the least significant digit of N. For Example :lastDigitOf(1234) = 4.
  • power(A, B) : This function returns the value of AB. For Example: power(2,4) = 16.
  • numberOfDigits(N) : This function returns the number of digits in N. log10(N) + 1, gives us the number of digits in N. For Example: numberOfDigits(1234) = log10(1234) + 1 = 4
  • getReversedNumber(N) = This is a recursive function, which reverses the sequence of digits of N and returns it to the caller function.
For Example
  • getReversedNumber(1234) = lastDigitOf(1234) x power(10, numberOfDigits(1234/10)) + getReversedNumber(1234/10)
  • getReversedNumber(1234) = 4 x power(10, numberOfDigits(123)) + getReversedNumber(123)
  • getReversedNumber(1234) = 4 x power(10, 3) + 321
  • getReversedNumber(1234) = 4 x 1000 + 321
  • getReversedNumber(1234) = 4321

Java program Reverse digits of a number using recursion

Java program Reverse digits of a number using recursion

package com.tcc.java.programs;
 
import java.io.*;
import java.util.*;
 
public class ReverseNumberRecursion {
    public static void main(String[] args) {
        int number=0;
 System.out.println("Input an Integer");
 Scanner in = new Scanner(System.in);
 number = in.nextInt();
 System.out.print("Reversed Number : " + reverse(number));
    }
 
    public static int reverse(int number) {
        int lastDigit, numberOfDigits, sign = 1;
      
        if(number < 0){
            number = number * -1;
            sign = -1;
        }
        if(number < 10)
            return number*sign;
          
        lastDigit = number % 10;
        number = number / 10;
        /* log10(number) + 1 gives number of digits in number */
        numberOfDigits = (int) (Math.log10((double)number) + 1);
      
        return (int)(lastDigit*Math.pow((double)10,(doublumberOfDigits) 
         + reverse(number)) * sign;
    }
}

Output

Input an Integer
435203
Reversed Number : 302534

Input an Integer
4
Reversed Number : 4