Longest Path With Different Adjacent Characters LeetCode solution in JavaScript

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var longestPath = function (parent, s) {
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  const adjList = parent.reduce(
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    (adjList, parent, node) => {
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      if (parent < 0) return adjList;
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      adjList[parent].push(node);
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      return adjList;
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    },
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    new Array(parent.length).fill(0).map(() => [])
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  );
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  let longest = 1;
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  const getLongest = (node) => {
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    let maxChild1 = 0;
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    let maxChild2 = 0;
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    adjList[node].forEach((child) => {
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      const childLength = getLongest(child);
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      // child letter matches our node, so we can't use it
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      if (s[child] === s[node]) return;
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      // compare and update the longest two child paths
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      if (childLength > maxChild1) {
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        maxChild2 = maxChild1;
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        maxChild1 = childLength;
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      } else if (childLength > maxChild2) {
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        maxChild2 = childLength;
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      }
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    });
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    // longest loop
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    longest = Math.max(longest, maxChild1 + maxChild2 + 1);
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    // return longest path up the tree
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    return 1 + maxChild1;
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  };
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  getLongest(0);
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  return longest;
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};