Reverse the bits of a number and check if the number is palindrome or not

Carvia Tech | August 05, 2019 | 1 min read | 103 views


Palindrome - Wiki definition

A palindrome is a word, number, or other sequence of characters which reads the same backward as forward, such as madam, racecar or 101 in binary etc.

We need a mechanism to reverse all the bits of the given input number and compare if both the number looks same after bit reversal.

The following Java code does the same:

Bitwise Palindrome
public static void main(String[] args) {
        int originalNumber = 9;
        long numBitsReversed = reverseBitsV1(originalNumber);
        long result = originalNumber ^ numBitsReversed; (1)
        if (result == 0) {
            System.out.println("Number is Palindrome");
        } else {
            System.out.println("Number is not Palindrome");
        }
    }

public static int reverseBitsV1(int number) {
    int reverse = 0;
    while (number != 0) {
        reverse <<= 1;  //left shift `reverse` by 1
        reverse |= (number & 1);   //Copy the rightmost bit of `number` into `reverse`
        number >>= 1;  //right shift `number` by 1
    }
    return reverse;
}
1 Just comparing of both numbers are same or not

Slightly different variant of reverse bit could be below code:

public static int reverseBitsV2(int number) {
    int reverse = 0;
    //Traversing bits of 'number' from the right and pushing it into left of `reverse` number
    while (number > 0) {
        reverse <<= 1; //Bitwise left shift 'reverse' by 1
        if ((number & 1) == 1) //if current bit is '1'
            reverse ^= 1; //Bitwise right shift 'number' by 1
        number >>= 1;
    }
    return reverse;
}

Functionality wise both are same.


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