Array With Elements Not Equal to Average of Neighbors LeetCode solution in JavaScript

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var rearrangeArray = function (nums) {
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  let arr = [],
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    res = [];
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  for (let q of nums) arr[q] = 1;
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  let l = 0,
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    r = arr.length - 1;
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  while (l <= r) {
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    while (!arr[l]) l++;
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    while (!arr[r]) r--;
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    if (l <= r) res.push(l++);
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    if (l <= r) res.push(r--);
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  }
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  return res;
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};