using System;

using System.Collections.Generic;

public class Program

{

    public class DbEntity

    {

        public string FirstName { get; set; }

​

        public string LastName { get; set; }

​

        public int Age { get; set; }

​

        public override string ToString()

        {

            return string.Format("{0} {1}, age {2}", FirstName, LastName, Age);

        }

    }

​

    public class DbGenerator

    {

        private static Random _random = new Random((int)DateTime.Now.Ticks);

​

        private static string[] _firstNames = new string[]

        {

            "Oliver",

            "Harry",

            "Jack",

            "George",

            "Noah",

            "Charlie",

            "Jacob",

            "Alfie",

            "Freddie"

        };

​

        private static string[] _lastNames = new string[]

        {

            "Smith",

            "Johnson",

            "Williams",

            "Jones",

            "Brown",

            "Davis",

            "Miller"

        };

​

        public IEnumerable<DbEntity> GetSequence(int count)

        {

            for (int i = 0; i < count; i++)

            {

                yield return new DbEntity

                {

                    FirstName = _firstNames[_random.Next(_firstNames.Length - 1)],

                    LastName = _lastNames[_random.Next(_lastNames.Length - 1)],

                    Age = _random.Next(18, 60)

                };

            }

        }

​

        public IEnumerable<DbEntity> GetSequence()

        {

            while(true)

            {

                yield return new DbEntity

                {

                    FirstName = _firstNames[_random.Next(_firstNames.Length - 1)],

                    LastName = _lastNames[_random.Next(_lastNames.Length - 1)],

                    Age = _random.Next(18, 60)

                };

            }

        }

    }

​

    public struct FirstLastKey

    {

        private readonly string _firstName;

        private readonly string _lastName;

​

        public FirstLastKey(string firstName, string lastName)

        {

            _firstName = firstName;

            _lastName = lastName;

        }

​

        public override bool Equals(object obj)

        {

            if(obj == null)

            {

                return false;

            }

            if(obj is FirstLastKey)

            {

                var objValue = (FirstLastKey)obj;

                if(this._firstName == objValue._firstName && this._lastName == objValue._lastName)

                {

                    return true;

                }

                return false;

            }

            return false;

        }

​

        public override int GetHashCode()

        {

            return (this._firstName.GetHashCode() >> 4) & this._lastName.GetHashCode();

        }

    }

    public class AgeKey

    {

        private readonly int _age;

        public AgeKey(int age)

        {

            _age = age;

        }

​

        public override bool Equals(object obj)

        {

            if(obj == null)

            {

                return false;

            }

            if(obj is AgeKey)

            {

                var objValue = (AgeKey)obj;

                return this._age == objValue._age;

            }

            return false;

        }

​

        public override int GetHashCode()

        {

            return this._age;

        }

    }

​

    public class Database

    {

        private readonly List<DbEntity> _entities = new List<DbEntity>();

        private readonly Dictionary<FirstLastKey, List<DbEntity>> _fnDict = new Dictionary<FirstLastKey, List<DbEntity>>();

        private readonly Dictionary<AgeKey, List<DbEntity>> _ageKeyDict = new Dictionary<AgeKey, List<DbEntity>>();

​

        public void AddRange(IEnumerable<DbEntity> entities)

        {

            _entities.AddRange(entities);

            foreach(var item in entities)

            {

                var firstLastKey = new FirstLastKey(item.FirstName, item.LastName);

                var ageKey = new AgeKey(item.Age);

                if(_fnDict.ContainsKey(firstLastKey))

                {

                    _fnDict[firstLastKey].Add(item);

                }

                else

                {

                    _fnDict.Add(firstLastKey, new List<DbEntity>() { item });

                }

                if(_ageKeyDict.ContainsKey(ageKey))

                {

                    _ageKeyDict[ageKey].Add(item);

                }

                else

                {

                    _ageKeyDict.Add(ageKey, new List<DbEntity>() { item });

                }

            }

        }

​

        public IList<DbEntity> FindBy(string firstName, string lastName)

        {

            var key = new FirstLastKey(firstName, lastName);

            if(_fnDict.ContainsKey(key))

            {

                return _fnDict[key];

            }

​

            return new DbEntity[] { };

        }

​

        public IList<DbEntity> FindBy(int age)

        {

            var key = new AgeKey(age);

            if(_ageKeyDict.ContainsKey(key))

            {

                return _ageKeyDict[key];

            }

            return new DbEntity[] { };

        }

    }

​

    public static void Main()

    {

        var dbGenerator = new DbGenerator();

        var db = new Database();

        db.AddRange(dbGenerator.GetSequence(10000));

​

        var items = db.FindBy("Jack", "Jones");

        Console.WriteLine(items.Count);

​

        var items2 = db.FindBy(30);

        Console.WriteLine(items2.Count);

    }

}