[JS] Number of 1 Bits

🔒 문제 (LeetCode 191)

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.

Constraints:

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

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

 

🌊 입출력

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.

 

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🔑 해결

🌌 알고리즘 - 비트 조작

n의 마지막 자릿수부터 올라가며 AND 연산으로 1인지 확인.

n & 1 = 1 or 0 이므로 1일 경우 카운트 증가 후 n의 모든 비트를 오른쪽으로 이동시켜 다음 자릿수를 검사.

/**
 * @param {number} n - a positive integer
 * @return {number}
 */
var hammingWeight = function(n) {
    let cnt = 0;
    
    while(n) {
        cnt += n & 1;
        n = n >>> 1;
    }
    
    return cnt;
};