LeetCode Number Complement

Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.

Note:
The given integer is guaranteed to fit within the range of a 32-bit signed integer.
You could assume no leading zero bit in the integer’s binary representation.
Example 1:
Input: 5
Output: 2
Explanation: The binary representation of 5 is 101 (no leading zero bits), and its complement is 010. So you need to output 2.
Example 2:
Input: 1
Output: 0
Explanation: The binary representation of 1 is 1 (no leading zero bits), and its complement is 0. So you need to output 0.

#coding=utf-8
class Solution(object):
    #朴素做法
    def findComplement(self, num):
        """
        :type num: int
        :rtype: int
        """
        s = bin(num)[2:]
        l = len(s)
        res  = []
        for i in xrange(l):
            if s[i] == '0':
                res.append('1')
            else:
                res.append('0')
        return int("".join(res),2)

class Solution2(object):
    def findComplement(self, num):
        """
        :type num: int
        :rtype: int
        """
        i = 1
        while i<= num:
            i = i << 1
        #now we get i > num
        return (i-1) ^ num
        # for example:
        # 10000 - 1 = 01111