day-188.cpp

/*
  Complement of Base 10 Integer


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.


*/

class Solution {
   public:
    int bitwiseComplement(int N) {
        if (N == 0) return 1;
        int numBits = floor(log2(N) + 1);
        return ((1 << numBits) - 1) ^ N;
    }
};