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

class Solution {
public:
    uint32_t reverseBits(uint32_t n) {
        uint32_t res;
        for (int i=0;i<32;i++)
        {
            res = res<<1 | (n&1);
            n = n>>1;
        }
        return res;
    }
};