Gray Code LeetCode solution in JavaScript

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/**
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 * @param {number} n
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 * @return {number[]}
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 */
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var grayCode = function (n) {
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  return binaryToInt(dfs(n, ["0", "1"]));
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};
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const dfs = (n, arr) => {
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  if (n === 1) return arr;
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  const revArr = [...arr].reverse();
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  addOneBefore("0", arr);
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  addOneBefore("1", revArr);
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  return dfs(n - 1, [...arr, ...revArr]);
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};
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const addOneBefore = (e, arr) => {
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  for (let i = 0; i < arr.length; i++) {
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    arr[i] = e + arr[i];
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  }
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};
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const binaryToInt = (arr) => {
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  for (let i = 0; i < arr.length; i++) {
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    arr[i] = parseInt(arr[i], 2);
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  }
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  return arr;
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};