描述
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:
0 <= N < 10^9
解析
根据题意，就是把 N 变成二进制的形态，然后将 1 变成 0 ，0 变成 1 ，将变换后的数字再转换回十进制。时间复杂度为 O(N)，空间复杂度为 O(N)，N 是二进制的位数。可以直接使用 python 的内置函数，按照上面的思路进行即可。
解答
class Solution(object):
def bitwiseComplement(self, N):
"""
:type N: int
:rtype: int
"""
result = ""
nbins = bin(N)[2:]
for i in nbins:
result += str(int(i)^1)
return int(result, 2)
运行结果
Runtime: 16 ms, faster than 77.81% of Python online submissions for Complement of Base 10 Integer.
Memory Usage: 11.7 MB, less than 79.49% of Python online submissions for Complement of Base 10 Integer.
解析
根据题意，我们还可以进行二进制的位运算和加法运算，先拿到 n 的二进制字符串 b ，然后从后向前一位一位计算补码数字的十进制大小，将其加入结果 result ，最后返回即可。
解答
class Solution(object):
def bitwiseComplement(self, n):
"""
:type n: int
:rtype: int
"""
b = bin(n)[2:]
result = 0
for i in range(len(b)-1, -1, -1):
result += (int(b[i])^1) * pow(2, len(b)-1-i)
return result
运行结果
Runtime: 20 ms, faster than 40.00% of Python online submissions for Complement of Base 10 Integer.
Memory Usage: 13.4 MB, less than 56.84% of Python online submissions for Complement of Base 10 Integer.
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