I'm doing a few challenges and I found this one on Codility:

A binary gap within a positive integer N is any maximal sequence of consecutive zeros that is surrounded by ones at both ends in the binary representation of N.

For example, number 9 has binary representation 1001 and contains a binary gap of length 2. The number 529 has binary representation 1000010001 and contains two binary gaps: one of length 4 and one of length 3. The number 20 has binary representation 10100 and contains one binary gap of length 1. The number 15 has binary representation 1111 and has no binary gaps. The number 32 has binary representation 100000 and has no binary gaps.

Write a function:

function solution(N);

that, given a positive integer N, returns the length of its longest binary gap. The function should return 0 if N doesn't contain a binary gap.

For example, given N = 1041 the function should return 5, because N has binary representation 10000010001 and so its longest binary gap is of length 5. Given N = 32 the function should return 0, because N has binary representation '100000' and thus no binary gaps.

Write an efficient algorithm for the following assumptions:

N is an integer within the range [1..2,147,483,647].

I have 3 solutions (one I found, another I wrote, and the 3rd was based on improvements made to mine)

function solution1(N) {
  const binaryString = N.toString(2);
  const start = '10';
  const end = '01';
  let startIndex = binaryString.indexOf(start);
  let endIndex = -1;
  let binaryGap = 0;
  // Remember that N is the
  // input number, and when you iterate over its binary representation, its always
  // log(N).
  while (startIndex >= 0) {
    endIndex = binaryString.indexOf(end, startIndex);
    if (endIndex < 0) {
    const tempGap = endIndex - startIndex;
    binaryGap = tempGap > binaryGap ? tempGap : binaryGap;
    startIndex = binaryString.indexOf(start, endIndex + 1);
    endIndex = -1;
  return binaryGap;
function solution2(n){
    const results = n.toString(2).split("1").slice(1)
    return results.reduce((acc,next,index)=>(next.length>acc && index<results.length-1  ? next.length : acc) ,0)
const solution3 = (n) => n.toString(2).split("1").slice(1,-1).reduce((acc,next,index)=>(next.length>acc ? next.length : acc) ,0)

All seem to be correct (and the solution 2 and 3 passed the test), and the solution 1, according to JSBench is slightly better, but because in the real-world every time we write code we don't test it to see which version is faster, I am curious about which solution is the most elegant and which one would you pick on a real-world scenario (if any one of them fails the challenge you can explain why, but I would love to still hear which one is the best and why, is it because is simpler to maintain/understand, more readable, declarative vs imperative, etc).


1 Answer 1


All your solutions involve converting the number to a string. That is more likely to impact performance than any of the other operations you perform.

If you keep the input as a number, you should be able to avoid allocating any new objects, including strings, which will improve your code's performance.


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