Problem
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.
Solution
Solution 1: XOR
Watch out the corner case when num is 0.
class Solution:
def bitwiseComplement(self, num: int) -> int:
if num == 0:
return 1
c = 1
n = num
while n:
c *= 2
n >>= 1
return num ^ (c - 1)
Solution 2:
x = 2 * x + 1
1 = 1
1*2 + 1 = 3 = 11
3*2 + 1 = 7 = 111
7*2 + 1 = 15 = 1111
class Solution:
def bitwiseComplement(self, num):
x = 1
while x < num: x = 2 * x + 1
return x - num