【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 == ‘1‘:
                res += ‘0‘
                continue
            res += ‘1‘
        return int(res,2)