Count Binary Substrings LeetCode solution in JavaScript

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/**
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 * find all bit switches '01' and '10'.
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 * From each one expand sideways: i goes left, j goes right
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 * Until:
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 * if '01' -> i,j != 0,1
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 * if '10' -> i,j != 1,0
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 * and within input boundaries
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 */
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var countBinarySubstrings = function (s) {
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  let i = 0;
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  const n = s.length;
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  let count = 0;
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  while (i < n - 1) {
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    if (s[i] != s[i + 1]) {
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      if (s[i] === "0") {
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        count += countZeroOnes(s, i, true);
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      } else {
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        count += countZeroOnes(s, i, false);
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      }
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    }
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    i++;
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  }
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  return count;
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  // count the number of valid substrings substrings
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  function countZeroOnes(s, start, startsWithZero) {
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    let count = 0;
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    let i = start;
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    let j = start + 1;
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    const n = s.length;
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    if (startsWithZero) {
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      while (i >= 0 && j < n && s[i] === "0" && s[j] === "1") {
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        count++;
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        i--;
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        j++;
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      }
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    } else {
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      while (i >= 0 && j < n && s[i] === "1" && s[j] === "0") {
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        count++;
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        i--;
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        j++;
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      }
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    }
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    return count;
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  }
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};