How to Reverse an Integer in Java Without Using Arrays?

Java: Reverse Integer Without Using Array

This article explores how to reverse an integer in Java without resorting to arrays, using a concise algorithm.

Algorithm

The algorithm leverages the modulus (%) operator to extract the rightmost digit of the input integer. This digit is appended to a new variable, reversedNum.

Next, reversedNum is multiplied by 10 to create a vacant position at the right end. Simultaneously, the input integer is divided by 10 to remove the extracted digit.

The process is repeated until the input integer reaches zero.

Here's a step-by-step breakdown:

1. Extract rightmost digit: (input % 10)
2. Append digit to reversedNum: reversedNum = reversedNum * 10 (input % 10)
3. Remove extracted digit from input: input = input / 10
4. Repeat steps 1-3 until input is zero

Code Example:

<code class="java">while (input != 0) {
    reversedNum = reversedNum * 10 + input % 10;
    input = input / 10;   
}</code>

Reversing Odd Digits Only

To reverse odd digits only, extract every second digit using the modulus operator and shift it to the left by multiplying it by 10. Here's a sample code:

<code class="java">int reversedOdd = 0;
while (input > 0) {
    reversedOdd = reversedOdd * 100 + input % 100;
    input = input / 100;
}</code>

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