1009. Complement of Base 10 Integer

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https://leetcode.com/problems/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.

    Note:
    1. 0 <= N < 10^9
    2. This question is the same as 476: https://leetcode.com/problems/number-complement/
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    Intuition

    Complement can be found by XOR with 1 at each digit
    Left shift 1 and continue till 1 comes at most significant bit

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    Time - O(N)
    Space - O(1)
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