Number of Nodes in the Sub-Tree With the Same Label LeetCode solution in JavaScript

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var countSubTrees = function (n, edges, labels) {
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  const adj = [];
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  for (let i = 0; i < n; i++) {
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    adj[i] = [];
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  }
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  for (const [u, v] of edges) {
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    adj[u].push(v);
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    adj[v].push(u);
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  }
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  const resCount = new Array(n).fill(0);
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  dfs(0, -1);
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  return resCount;
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  function dfs(node, parent) {
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    const label = labels.charCodeAt(node) - 97;
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    const charCount = new Array(26).fill(0);
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    charCount[label] = 1;
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    for (const childNode of adj[node]) {
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      if (childNode == parent) continue;
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      const subCount = dfs(childNode, node);
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      for (let i = 0; i < 26; i++) {
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        charCount[i] += subCount[i];
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      }
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    }
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    resCount[node] = charCount[label];
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    return charCount;
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  }
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};