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 as00111001011110000010100101000000).
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.

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public class Solution {
    // you need treat n as an unsigned value
    public int reverseBits(int n) {
        int ret = 0;
        for(int i = 0; i < 32; i++){
            ret += (n & 0x1);
            if(i < 31){
                n = n>>1;
                ret = ret<<1;
            }
        }
        return ret;
    }
}