Longest Palindrome by Concatenating Two Letter Words LeetCode solution in JavaScript

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var longestPalindrome = function (words) {
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  const n = words.length;
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  const map = new Map();
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  let len = 0;
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  for (const word of words) {
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    const backward = word.split("").reverse().join("");
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    if (map.has(backward)) {
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      len += word.length * 2;
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      map.set(backward, map.get(backward) - 1);
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      if (map.get(backward) === 0) map.delete(backward);
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    } else {
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      if (!map.has(word)) map.set(word, 0);
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      map.set(word, map.get(word) + 1);
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    }
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  }
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  let maxLenSelfPalindrome = 0;
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  for (const word of map.keys()) {
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    if (isPalindrome(word)) {
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      maxLenSelfPalindrome = Math.max(maxLenSelfPalindrome, word.length);
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    }
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  }
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  return len + maxLenSelfPalindrome;
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  function isPalindrome(word) {
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    let left = 0;
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    let right = word.length - 1;
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    while (left < right) {
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      if (word[left] != word[right]) return false;
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      left++;
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      --right;
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    }
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    return true;
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  }
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};