How to Reverse Only Odd Numbers in an Integer in Java?

Java: Reverse an Int Value Without Using Array

Explanation of the Code:

The code snippet you provided uses a while loop to reverse an integer value. Here's how it works:

• ReversedNum Multiplication: The variable reversedNum is initially set to 0. In each iteration of the loop, we multiply reversedNum by 10 to "shift" the existing reversed number one digit to the left.
• Input Modding: We calculate input % 10 to extract the rightmost digit of the input number. This gives us the digit to be added to the reversed number.
• Adding to ReversedNum: The extracted rightmost digit is added to reversedNum to form the reversed number.
• Division of Input: Finally, we divide the input number by 10 to remove the rightmost digit and continue the process with the remaining digits.

Reversing Only Odd Numbers:

To reverse only odd numbers in a given integer, you can use the following steps:

• Separate the even and odd digits into different variables.
• Reverse the odd digits using the above method.
• Combine the reversed odd digits with the original even digits.

Sample Code:

<code class="java">public static int reverseOdd(int input) {
    int even = 0;
    int odd = 0;

    // Separate even and odd digits
    while (input > 0) {
        int digit = input % 10;
        if (digit % 2 == 0) {
            even = even * 10 + digit;
        } else {
            odd = odd * 10 + digit;
        }
        input /= 10;
    }

    // Reverse odd digits
    odd = reverseInt(odd);

    // Combine reversed odd and original even digits
    return even + odd;
}

public static int reverseInt(int input) {
    long reversedNum = 0;
    long input_long = input;

    while (input_long != 0) {
        reversedNum = reversedNum * 10 + input_long % 10;
        input_long /= 10;
    }

    if (reversedNum > Integer.MAX_VALUE || reversedNum < Integer.MIN_VALUE) {
        throw new IllegalArgumentException();
    }
    return (int) reversedNum;
}</code>

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