How to Reverse an Integer in Java Without Using Arrays or Strings?

Java Reverse an Int Value Without Using Array

Understanding the Algorithm

To reverse an integer without using arrays or strings, we employ a simple yet effective algorithm. Let's break down its key steps:

1. Extract Rightmost Digit: We extract the rightmost digit of the input integer using the modulus operator (%). For example, for 1234, 1234 % 10 will result in 4.
2. Add to Reversed Number: We add the extracted digit to a variable (reversedNum) that will accumulate the reversed value. For the example above, reversedNum becomes 4.
3. Multiply Reversed Number by 10: To make room for the next digit, we multiply reversedNum by 10. In our case, this becomes 4 * 10 = 40.
4. Remove the Extracted Digit: We divide the input integer by 10 (1234 / 10) to remove the rightmost digit. This results in 123.
5. Repeat the Process: We repeat steps 1-4 until the input integer becomes 0.

Code Implementation

<code class="java">while (input != 0) {
    reversedNum = reversedNum * 10 + input % 10; // Add digit to reversed number
    input = input / 10; // Remove the rightmost digit
}</code>

Reversing Odd Digits Only

To reverse only odd digits, we can modify the algorithm by extracting odd digits only and adding them to reversedNum. We can use the % 2 == 1 condition to check for odd digits:

<code class="java">while (input != 0) {
    if (input % 10 % 2 == 1) {
        reversedNum = reversedNum * 10 + input % 10; // Add odd digit to reversed number
    }
    input = input / 10; // Remove the rightmost digit
}</code>

By following these principles and incorporating them into the code, we can effectively reverse integers without relying on arrays or strings. It's a valuable exercise that demonstrates problem-solving skills and numerical manipulation techniques.

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