190. 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.

https://discuss.leetcode.com/topic/42572/sharing-my-2ms-java-solution-with-explanation

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++){
            res <<= 1;
            if((n & 1) == 1) res ++;
            n >>=1;
        }
        return res;
    }
}