Employee Importance LeetCode solution in Java

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class Solution {
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  private Map<Integer, Integer> idToIndex;
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  private void populateIdToIndexMap(List<Employee> employees) {
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    for (int idx = 0; idx < employees.size(); idx++) {
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      idToIndex.put(employees.get(idx).id, idx);
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    }
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  }
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  private int dfsGetImportance(List<Employee> employees, int id) {
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    int currEmpIdx = idToIndex.get(id);
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    Employee currEmp = employees.get(currEmpIdx);
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    int totalImportance = currEmp.importance;
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    for (int child : currEmp.subordinates) {
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      totalImportance += dfsGetImportance(employees, child);
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    }
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    return totalImportance;
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  }
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  public int getImportance(List<Employee> employees, int id) {
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    if (employees == null || employees.size() < 1) {
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      return 0;
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    }
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    idToIndex = new HashMap<>();
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    populateIdToIndexMap(employees);
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    return dfsGetImportance(employees, id);
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  }
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}