Number of 1 Bits.md

Type: [[Bit Manipulation Questions (C)]]

Easy (11/30/2022)

Leet code link: https://leetcode.com/problems/number-of-1-bits/description/

Notes: mod % 2 of 1 and 0 will give the same number. >> shifts the bit to the left and so does // by 2. (n-1) remove 1 and & compliment will make it zero.

191. Number of 1 Bits

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

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.

Solution 1 (mod 2):

   def hammingWeight(self, n: int) -> int:
       count = 0
       while n:
           count += n % 2
           n = n >> 1
       return count

Solution 2 (& by n-1):

	def hammingWeight(self, n: int) -> int:
        res = 0
        while n:
            n &= n - 1
            res += 1
	        return res