Leetcode 190. Reverse Bits

Reverse bits of a given 32 bits unsigned integer.

Since Java doesn’t have unsigned numbers, this task becomes a way more interesting. The simplest way would be to operate with bits, I’ve added a bunch of comments to the code to make it clear

public class Solution {
    // you need treat n as an unsigned value
    public int reverseBits(int n) {
        int res = 0;
        for (int i = 0; i < 32; i++) {
            // shift to the left, i.e. ...001 is changed into ...010
            res <<= 1; 
            // n&1 - keep 1 at the end of n if it ends with 1
            // | if n ends with 1, then res is also ends with 1
            res = res | (n & 1); 
            n >>= 1; // shift n to the right for 1 position
        }
        return res;
        
    }
}