191. Number of 1 Bits

Problem

Tags: Bit Manipulation

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.

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

Code

C

// 191. Number of 1 Bits (5/8/54369)
// Runtime: 3 ms (40.72%) Memory: 5.43 MB (38.83%) 

int hammingWeight (uint32_t n) {
    uint8_t count = 0;
    
    while (n) {
        n = n & (n - 1);
        count++;
    }
    
    return count;
}

GO

// 191. Number of 1 Bits (5/9/54369)
// Runtime: 0 ms (90.80%) Memory: 1.84 MB (43.77%) 

func hammingWeight(num uint32) int {
    count := 0
    
    for num > 0 {
        num = num & (num - 1)
        count++
    }
    
    return count
}

JS

// 191. Number of 1 Bits (3/10/53745)
// Runtime: 80 ms (57.00%) Memory: 40.46 MB (94.65%) 

/**
 * @param {number} n - a positive integer
 * @return {number}
 */
function hammingWeight(n) {
    return [...n.toString(2)].filter((x) => x === "1").length;
}

TS

// 191. Number of 1 Bits (5/20/54369)
// Runtime: 109 ms (33.99%) Memory: 44.26 MB (87.93%) 

function hammingWeight(n: number): number {
    let count = 0;
    
    while (n) {
        count++;
        n = n & (n - 1);
    }
    
    return count;
};