05. Complement of Base 10 Integer.cpp

/*
Complement of Base 10 Integer
=============================

Solution
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
This question is the same as 476: https://leetcode.com/problems/number-complement/

Hint #1  
A binary number plus its complement will equal 111....111 in binary. Also, N = 0 is a corner case.
*/

/* Language: C++ 
==================
*/

class Solution
{
public:
  int bitwiseComplement(int n)
  {
    int num = 0;
    if (n == 0)
      return 1;
    while (num < n)
    {
      num = (num << 1) | 1;
    }
    return ~n & num;
  }
};