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?

Related problem: Reverse Integer

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

# @param {Integer} n, a positive integer
# @return {Integer}
def reverse_bits(n)
    2**(32-(n.to_s(2)).length())*n.to_s(2).reverse!.to_i(2)
end