Reverse Bits

Reverse bits of a given 32 bits unsigned integer.

For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192 (represented in binary as 00111001011110000010100101000000).

Follow up: If this function is called many times, how would you optimize it?

Related problem: Reverse Integer

Credits:Special thanks to @ts for adding this problem and creating all test cases.

Solution

public class Solution {
      public int reverseBits(int n) {
        int start = 0;
        int end = 31;

        while (start < end) {
            n = swap(n, start, end);
            start++;
            end--;
        }

        return n;
    }

    private int swap(int n, int i, int j) {
        int a = (n >> i) & 1;
        int b = (n >> j) & 1;

        if ((a ^ b) != 0) {
            n ^= (1 << i) | (1 << j);
        }

        return n;

    }
}