Maximum Product of the Length of Two Palindromic Subsequences LeetCode solution in JavaScript

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/**
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 * @param {string} s
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 * @return {number}
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 */
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var maxProduct = function (s) {
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  const n = s.length;
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  let map = new Map();
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  let res = 0;
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  for (let mask = 1; mask < 2 ** n; mask++) {
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    let str = "";
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    for (let i = 0; i < n; i++) {
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      if (mask & (1 << i)) {
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        str += s.charAt(n - 1 - i);
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      }
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    }
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    if (isPalindrom(str)) {
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      let length = str.length;
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      map.set(mask, length);
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    }
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  }
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  map.forEach((l1, m1) => {
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    map.forEach((l2, m2) => {
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      if ((m1 & m2) == 0) {
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        res = Math.max(res, l1 * l2);
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      }
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    });
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  });
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  return res;
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};
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function isPalindrom(str) {
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  let l = 0;
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  let r = str.length - 1;
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  while (l < r) {
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    if (str.charAt(l) != str.charAt(r)) {
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      return false;
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    }
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    l++;
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    r--;
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  }
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  return true;
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}