Number of 1 Bits with Javascript

Question

Question: Write a function that takes an unsigned integer and returns the number of '1' bits it has (also known as the Hamming weight).

Example 1:

Input: n = 00000000000000000000000000001011

Output: 3

Explanation: The input binary string 00000000000000000000000000001011 has a total of three '1' bits.

My Code

var hammingWeight = function(n) {
    for (i=0; i<32; i++) {
        var mask = 1;
        var count = 0;
        if ((mask & n) != 0 ) {            
            mask <<= 1;
            count++;
        }    
        return count;
    }
};

Test Case:

00000000000000000000000000001011
00000000000000000000000010000000
11111111111111111111111111111101

Expected Output:

3
1
31

Output:

1
0
1

What did I do wrong with my code?

Does this answer your question? [Efficiently count the number of bits in an integer in JavaScript](https://stackoverflow.com/questions/43122082/efficiently-count-the-number-of-bits-in-an-integer-in-javascript) — GOTO 0, Nov 28 '21 at 21:19
Not the same approach but it's related to the subject. Thanks for suggesting! — SelfTaughtLooking4Job, Nov 28 '21 at 21:27

fin444 · Accepted Answer · 2021-11-28T21:30:49.657

3

You have a few issues here:

You are redefining count and mask inside of your for loop.
You are returning after the first iteration of the loop, instead of waiting for the whole thing to count up.
You only shift mask if a bit is 1.

Here is a corrected function:

var hammingWeight = function(n) {
    var count = 0;
    var mask = 1;
    for (i=0; i<32; i++) {
        if ((mask & n) != 0 ) {            
            count++;
        }
        mask <<= 1;
    }
    return count;
};

edited Nov 28 '21 at 21:30

answered Nov 28 '21 at 21:05

fin444

725
2
14
27

1

Mask should also go with the count as well. – StereoBucket Nov 28 '21 at 21:05
1

And to get correct results, shifting the `mask` should be outside of the `if` – FZs Nov 28 '21 at 21:13

score 1 · Answer 2 · answered Nov 28 '21 at 21:46

A shorter way to write this could be:

const hammingWeight = value => [...value].filter(f => f == 1).length;

Explanation:

[...value] this will create an array of 0's and 1's based on your string

.filter(f => f == 1) will filter the array, keeping only the 1 values

.length gives you the length of the filtered array

Number of 1 Bits with Javascript

2 Answers2