位运算（3）——Reverse Bits

翻转32位无符号二进制整数

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?

 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 = res + (n & 1);
             if(i < 31) {
                 res = res << 1;
             }
             n = n >> 1;
         }
         return res;
     }
 }

另一种写法：

 　　public int reverseBits(int n) {
         int res = 0;
         for(int i=0; i<32; i++) {
             if((n & 1) == 1) {
                 res = (res << 1) + 1;
             } else {
                 res = res << 1;
             }
             n = n >> 1;
         }
         return res;
     }

思路都是从右到左判断0/1，加到res。