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.

class Solution {
public:
    uint32_t reverseBits(uint32_t n) {
    //不是按位取反 而是颠前后顺序
        uint32_t i,res=0;
        for(i=0;i<=31;i++)
        {
            res|=((n>>i)&1)<<(31-i);
        }
        return res;
    }
};