using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

            var person1 = new Person() {id = 1, name = "Bob" };

            var person2 = new Person() {id = 2, name = "Ted" };

            var person3 = new Person() {id = 3, name = "Will_1" };

            var person4 = new Person() {id = 4, name = "Will_2" };

​

            person1.documents.Add(new IdentificationDocument() { number = "123" });

            person2.documents.Add(new IdentificationDocument() { number = "456" });

            person3.documents.Add(new IdentificationDocument() { number = "789" });

            person3.documents.Add(new IdentificationDocument() { number = "147" });

            person4.documents.Add(new IdentificationDocument() { number = "789" }); //duplicate

            person4.documents.Add(new IdentificationDocument() { number = "147" }); //duplicate

​

            var personList1 = new List<Person>();

​

            personList1.Add(person1);

            personList1.Add(person2);

            personList1.Add(person3);

            personList1.Add(person4);

            //More data for performance test

            for (int i = 0; i < 20000; i++)

            {

                var personx = new Person() { id = i, name = Guid.NewGuid().ToString() };

                personx.documents.Add(new IdentificationDocument() { number = Guid.NewGuid().ToString() });

                personx.documents.Add(new IdentificationDocument() { number = Guid.NewGuid().ToString() });

                personList1.Add(personx);

            }

            var result = new List<Person>();

​

            foreach (var person in personList1)

            {

                if (!result.Any(r => r.documents.SelectMany(rd => rd.number)

                    .Intersect(person.documents.SelectMany(pd => pd.number))

                    .Any()))

                {

                    result.Add(person);

                }

            }

​

            result.ForEach(r => Console.WriteLine(r.id + " " +r.name));

        //Expected result:

        //1 Bob

        //2 Ted

        //3 Will_1

        //Note: Select instead SelectMany works, but is too slow when i have many elements (> 200 thousand)

​

    }

    public class Person

    {

        public int id { get; set; }

        public string name { get; set; }

        public List<IdentificationDocument> documents { get; set; }

​

        public Person()

        {

            documents = new List<IdentificationDocument>();

        }

    }

​

    public class IdentificationDocument

    {

        public string number { get; set; }

    }

}