[LeetCode] Challenge log 476

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476. Number Complement
  1. Use XOR 11111… to flip bit.
  2. Use Mask to decide which bits are 1s.

Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.

Note:

  1. The given integer is guaranteed to fit within the range of a 32-bit signed integer.
  2. You could assume no leading zero bit in the integer’s binary representation.

Example 1:

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Input: 5
Output: 2
Explanation: The binary representation of 5 is 101 (no leading zero bits), and its complement is 010. So you need to output 2.

Example 2:

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Input: 1
Output: 0
Explanation: The binary representation of 1 is 1 (no leading zero bits), and its complement is 0. So you need to output 0.
Soulution:
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class Solution:
    def findComplement(self, num):
        """
        :type num: int
        :rtype: int
        """
        mask = 1
        while mask <= num:
            mask = mask << 1
        mask -= 1
        return num ^ mask
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class Solution:
    def findComplement(self, num):
        """
        :type num: int
        :rtype: int
        """
        mask = 1
        res = 0
        for i in range(32):
            if 2**i > num: break
            if mask & num == 0: res += 2**i
            mask = mask << 1
        return res
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