LeetCodeEasy- [Interview Question 15. Number of 1 in Binary]

Please implement a function, input an integer, and output the number of 1s in the binary representation of the number. For example, representing 9 as binary is 1001, and 2 bits are 1. Therefore, if you enter 9, the function outputs 2.

Example 1:

Input: 00000000000000000000000000001011
Output: 3
Explanation: In the input binary string 00000000000000000000000000001011, there are three bits of '1'.

Example 2:

Input: 00000000000000000000000010000000
Output: 1
Explanation: In the input binary string 00000000000000000000000010000000, there is a total of '1'

Example 3:

Input: 11111111111111111111111111111101
Output: 31
Explanation: In the input binary string 11111111111111111111111111111101, a total of 31 bits are '1'.

Source: LeetCode
Link: https://leetcode-cn.com/problems/er-jin-zhi-zhong-1de-ge-shu-lcof
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Idea 1: Judging odd and even numbers, dividing by 2

class Solution:
    def hammingWeight(self, n: int) -> int:
        ans = 0
        while n:
            if n & 1 == 1:
                ans += 1
            n //= 2
        return ans

Idea 2: Ingenious use (n-1) & n

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