Longest Word in Dictionary LeetCode solution in Java

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class Solution {
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  private class Node {
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    Node[] sub;
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    Node() {
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      sub = new Node[26];
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    }
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  }
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  Node root;
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  StringBuilder ans;
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  private void buildTire(String word) {
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    Node temp = root;
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    int n = word.length();
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    for (int i = 0; i < n - 1; i++) {
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      int index = word.charAt(i) - 'a';
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      if (temp.sub[index] == null) return;
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      temp = temp.sub[index];
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    }
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    int index = word.charAt(n - 1) - 'a';
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    temp.sub[index] = new Node();
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    if (word.length() > ans.length()) ans = new StringBuilder(word);
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  }
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  public String longestWord(String[] words) {
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    this.ans = new StringBuilder();
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    this.root = new Node();
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    PriorityQueue<String> pq = new PriorityQueue<>();
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    pq.addAll(Arrays.asList(words));
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    while (!pq.isEmpty()) buildTire(pq.poll());
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    return ans.toString();
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  }
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}