ReverseBits.java

public class Solution {
    // you need treat n as an unsigned value
    public int reverseBits(int n) {
        for (int i = 0; i < 16; i++) {
            n = swapBit(n, i, 32-1-i);
        }
        
        return n;
    }
    
    public int swapBit(int n, int i, int j) {
        int a = (n >> i) & 1;
        int b = (n >> j) & 1;
        if (a != b) {
            n ^= 1 << i | 1 << j;
        }
        
        return n;
    }
}