Number of 1 Bits

Category: Binary

Deadline: 2nd week (1/7 - 1/15)

Difficulty: Easy

Github: https://github.com/iamseokhyun/2022-algorithm-study/tree/master/binary/Numberof1Bits/

LeetCode link: https://leetcode.com/problems/number-of-1-bits/

Problem

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.

Solution

public class Solution
{
    public int HammingWeight(uint n)
    {
        int i = 0;

        for (int p = 0; p < 32; p++)
        {
            if (Convert.ToBoolean(n % 2))
            {
                i++;
            }

            n /= 2;
        }

        return i;
    }
}

Comment

• HammingWeight 문제. n을 2로 나눈 나머지, 즉 n을 이진법 표기하였을 때 마지막 자릿수가 1이라면 i++을 수행, n을 2로 나누어 자릿수를 한칸 오른쪽으로 옮겨주는 과정.
• i를 출력하면 uint n의 이진법 표기에서 1의 갯수를 알 수 있음.