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持续左移，每次插入n的最后一位，n保持右移
            res = res << 1;
            res = res + (n & 1);
            // n & 1：获取n的最后一位
            n = n >> 1;
        }
        return res;
    }
}