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class Solution {
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  int dfs(List<List<Integer>> al, boolean[] visited, int from) {
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    int change = 0;
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    visited[from] = true;
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    for (var to : al.get(from))
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      if (!visited[Math.abs(to)]) change += dfs(al, visited, Math.abs(to)) + (to > 0 ? 1 : 0);
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    return change;
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  }
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  public int minReorder(int n, int[][] connections) {
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    List<List<Integer>> al = new ArrayList<>();
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    for (int i = 0; i < n; ++i) al.add(new ArrayList<>());
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    for (var c : connections) {
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      al.get(c[0]).add(c[1]);
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      al.get(c[1]).add(-c[0]);
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    }
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    return dfs(al, new boolean[n], 0);
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  }
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}