Loud and Rich LeetCode solution in Java

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class Solution {
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  ArrayList<ArrayList<Integer>> adj = new ArrayList<>();
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  int res[];
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  public int[] loudAndRich(int[][] richer, int[] quiet) {
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    int n = quiet.length;
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    res = new int[n];
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    Arrays.fill(res, -1);
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    for (int i = 0; i < n; i++) adj.add(new ArrayList<Integer>());
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    for (int i = 0; i < richer.length; i++) {
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      if (adj.get(richer[i][1]) == null) adj.add(new ArrayList<>());
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      adj.get(richer[i][1]).add(richer[i][0]);
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    }
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    for (int i = 0; i < n; i++) dfs(i, quiet);
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    return res;
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  }
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  public int dfs(int node, int[] quiet) {
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    if (res[node] == -1) {
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      res[node] = node;
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      for (int v : adj.get(node)) {
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        int cand = dfs(v, quiet);
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        if (quiet[cand] < quiet[res[node]]) res[node] = cand;
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      }
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    }
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    return res[node];
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  }
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}