191. Number of 1 Bits

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191. Number of 1 Bits

Description

Given a positive integer n, write a function that returns the number of set bits in its binary representation (also known as the Hamming weight).

Example 1:

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Input: n = 11

Output: 3

Explanation:

The input binary string 1011 has a total of three set bits.

Example 2:

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Input: n = 128

Output: 1

Explanation:

The input binary string 10000000 has a total of one set bit.

Example 3:

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Input: n = 2147483645

Output: 30

Explanation:

The input binary string 1111111111111111111111111111101 has a total of thirty set bits.

Constraints:

  • 1 <= n <= 2^31 - 1

Follow up: If this function is called many times, how would you optimize it?

Hints/Notes

  • 2025/01/01
  • bit manipulation
  • No solution from 0x3F

Solution

Language: C++

Low bit:

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class Solution {
public:
    int hammingWeight(int n) {
        int res = 0;
        while (n) {
            n &= n - 1;
            res++;
        }
        return res;
    }
};
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class Solution {
public:
    int hammingWeight(int n) {
        int res = 0;
        while (n) {
            res += n % 2;
            n /= 2;
        }
        return res;
    }
};