LeetCode: Employee-importance BFS

Question

You are given a data structure of employee information, which includes the employee's unique id, his importance value and his direct subordinates' id.

For example, employee 1 is the leader of employee 2, and employee 2 is the leader of employee 3. They have importance value 15, 10 and 5, respectively. Then employee 1 has a data structure like [1, 15, [2]], and employee 2 has [2, 10, [3]], and employee 3 has [3, 5, []]. Note that although employee 3 is also a subordinate of employee 1, the relationship is not direct.

Now given the employee information of a company, and an employee id, you need to return the total importance value of this employee and all his subordinates.

Example 1:

Input: [[1, 5, [2, 3]], [2, 3, []], [3, 3, []]], 1 Output: 11 Explanation: Employee 1 has importance value 5, and he has two direct subordinates: employee 2 and employee 3. They both have importance value 3. So the total importance value of employee 1 is 5 + 3 + 3 = 11.

Note:

One employee has at most one direct leader and may have several subordinates. The maximum number of employees won't exceed 2000.

Please comment about performance.

using System.Collections.Generic;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace GraphsQuestions
{
    /// <summary>
    /// https://leetcode.com/problems/employee-importance/
    /// </summary>
    [TestClass]
    public class EmployeeImportanceBFS
    {
        [TestMethod]
        public void ChildrenSumTo30Test()
        {
            List<Employee> employees = new List<Employee>();
            Employee one = new Employee { Id = 1, Importance = 15 };
            Employee two = new Employee { Id = 2, Importance = 10 };
            one.Subordinates.Add(two.Id);
            Employee three = new Employee { Id = 3, Importance = 5 };
            two.Subordinates.Add(three.Id);
            employees.Add(one);
            employees.Add(two);
            employees.Add(three);
            Assert.AreEqual(30, GetImportance(employees, 1));
        }

        [TestMethod]
        public void ChildrenSumTo11Test()
        {
            List<Employee> employees = new List<Employee>();
            Employee one = new Employee { Id = 1, Importance = 5 };
            Employee two = new Employee { Id = 2, Importance = 3 };
            Employee three = new Employee { Id = 3, Importance = 3 };
            one.Subordinates.Add(three.Id);
            one.Subordinates.Add(two.Id);
            employees.Add(one);
            employees.Add(two);
            employees.Add(three);
            Assert.AreEqual(11, GetImportance(employees, 1));
        }

        int GetImportance(IList<Employee> employees, int id)
        {
            Dictionary<int, Employee> idToEmployee = new Dictionary<int, Employee>();
            foreach (var employee in employees)
            {
                idToEmployee.Add(employee.Id, employee);
            }

            int result = 0;
            if (employees == null || employees.Count == 0)
            {
                return result;
            }
            Queue<Employee> Q = new Queue<Employee>();
            Q.Enqueue(idToEmployee[id]);
            while (Q.Count > 0)
            {
                var current = Q.Dequeue();
                result += current.Importance;
                foreach (var childIdSubordinate in current.Subordinates)
                {
                    if (idToEmployee.ContainsKey(childIdSubordinate))
                    {
                        Q.Enqueue(idToEmployee[childIdSubordinate]);
                    }
                }
            }

            return result;
        }
    }



    // Employee info
    class Employee
    {
        public Employee()
        {
            Subordinates = new List<int>();
        }
        // It's the unique ID of each node.
        // unique id of this employee
        public int Id { get; set; }
        // the importance value of this employee
        public int Importance { get; set; }
        // the id of direct subordinates
        public List<int> Subordinates { get; set; }
    }

}

Answer 1

You'll have to have this check before the initialization of the dictionary:

  if (employees == null || employees.Count == 0)
  {
    return 0;
  }

or else the initialization of the dictionary may throw if employees == null

---

You can initialize the dictionary this way:

Dictionary<int, Employee> idToEmployee = employees.ToDictionary(e => e.Id);

---

Instead of:

if (idToEmployee.ContainsKey(childIdSubordinate))
  {
    Q.Enqueue(idToEmployee[childIdSubordinate]);
  }

You can do:

      if (idToEmployee.TryGetValue(childIdSubordinate, out Employee subordinate))
      {
        Q.Enqueue(subordinate);
      }