Leetcode 191. Number of 1 Bits (Python)

Write a function that takes an unsigned integer and returns the number of '1' bits it has (also known as the Hamming weight).

Note:

  • Note that in some languages, such as Java, there is no unsigned integer type. In this case, the input will be given as a signed integer type. It should not affect your implementation, as the integer's internal binary representation is the same, whether it is signed or unsigned.
  • In Java, the compiler represents the signed integers using 2's complement notation. Therefore, in Example 3, the input represents the signed integer. -3.

Example 1:

Input: n = 00000000000000000000000000001011
Output: 3
Explanation: The input binary string 00000000000000000000000000001011 has a total of three '1' bits.

Example 2:

Input: n = 00000000000000000000000010000000
Output: 1
Explanation: The input binary string 00000000000000000000000010000000 has a total of one '1' bit.

Example 3:

Input: n = 11111111111111111111111111111101
Output: 31
Explanation: The input binary string 11111111111111111111111111111101 has a total of thirty one '1' bits.

Constraints:

  • The input must be a binary string of length 32.

Simply use bitwise manipulation. Set temp bit as 1, and it will shift when iterating the input number. 1 and 1 is 1. 1 and 0 is 0. So, the target bit can be saved and the other bits are removed. Then, just check if this target bit is 1 or 0.
Again, NO NEED TO CONVERT INPUT NUMBER TO STRING.

class Solution(object):
    def hammingWeight(self, n):
        """
        :type n: int
        :rtype: int
        """
        and_bit = 1
        count = 0
        for i in range(32):
            and_bit = and_bit << i
            bit_value = (n & and_bit) >> i
            if bit_value == 1:
                count += 1
            and_bit = 1    
            
        return count

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