CODEWITHSUNDEEP
javascriptbinary
Foreever
Foreever

Reputation: 7468

How to find the number of 1's in a binary representation of a number?

From other searches, I found that this problem is called 'Hamming Weight' or 'Population Count'. There are lot of answers out there given with so many statistics? I need to find the solution in a simple way? Complexity is not a big deal. Is there any in-built function in JavaScript like Java's Integer.bitCount?

I'm currently doing this as follows. 

var binary = 3;
var original = binary;
var count = 0;
while(binary>0)
{
    binary = binary >> 1 << 1;
    if(original-binary==1)
        count++;
    original = binary >> 1;
    binary = original;
}

Is there a better, more simple as well as elegant way for this?

Upvotes: 5

Views: 9106

Answers (5)

Naveen Gupta
Naveen Gupta

Reputation: 286

  function numOfOnes(n) {
    if(n === 0) return n;
    return (n & 1) + numOfOnes(n >>= 1);
  }

Basically this approach belongs to recursive call.
It has the base condition when no number to evaluate.
Otherwise it calls itself on (n >>= 1) and add last digit (n & 1) to result.
eg. 7 has binary representation 111 = 1+1+1 = 3
17 has binary representation 10001 = 1+0+0+0+1 = 2

Upvotes: 1

Anurag Sindhu
Anurag Sindhu

Reputation: 25

function countOnesInDecimal(num) {
  let count = 0;
  let binary = num.toString(2);
  const splitted = binary.split('');
  for (const iterator of splitted) {
    if (iterator === `1`) {
      count += 1;
    }
  }

  return count;
}
console.log(countOnesInDecimal(3));

Upvotes: 0

A-Sharabiani
A-Sharabiani

Reputation: 19329

A simple way without using built-in functions:

function f(n){
    let i = 0;
    do if(n&1) ++i; while(n>>=1)
    return i;
}

// example:
console.log(f(7)); // 3

Upvotes: 3

Duy Tran
Duy Tran

Reputation: 39

If you want to count 1 digit in binary representation we can use regular expression like this.

number.toString(2).match(/1/g).length

Upvotes: 3

Amarnath R Shenoy
Amarnath R Shenoy

Reputation: 5201

try this

var binary = 10;
var result = binary.toString(2); //Converts to binary
var count = result.split(1);//  count -1 is your answer
alert((result.split('1').length-1));

can also be written as 

(binary.toString(2).split('1').length-1)

toString(2)  : helps to split it in a base2 format which is binary, can do this in a range of 2- 36 (iam not sure about the range)

Upvotes: 6

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