【leetcode】1012. Complement of Base 10 Integer

题目如下：

Every non-negative integer N has a binary representation.  For example, 5 can be represented as "101" in binary, 11 as "1011" in binary, and so on.  Note that except for N = 0, there are no leading zeroes in any binary representation.

The complement of a binary representation is the number in binary you get when changing every 1 to a 0 and 0 to a 1.  For example, the complement of "101" in binary is "010" in binary.

For a given number N in base-10, return the complement of it's binary representation as a base-10 integer.

Example 1:

Input: 5
Output: 2
Explanation: 5 is "101" in binary, with complement "010" in binary, which is 2 in base-10.

Example 2:

Input: 7
Output: 0
Explanation: 7 is "111" in binary, with complement "000" in binary, which is 0 in base-10.

Example 3:

Input: 10
Output: 5
Explanation: 10 is "1010" in binary, with complement "0101" in binary, which is 5 in base-10.

Note:

1. 0 <= N < 10^9

解题思路：题目很简单，把Input转成二进制形式，然后对每一位取反，最后再转成十进制就可以了。

代码如下：

class Solution(object):
    def bitwiseComplement(self, N):
        """
        :type N: int
        :rtype: int
        """
        SN = bin(N)[2:]
        res = ''
        for i in SN:
            if i == '':
                res += ''
                continue
            res += ''
        return int(res,2)