using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class MyStringifiedNumberComparer : IEqualityComparer<string> {
    public bool Equals(string x, string y) {
        return (Int32.Parse(x) == Int32.Parse(y));
    }

    public int GetHashCode(string obj) {
        return Int32.Parse(obj).ToString().GetHashCode();
    }
}
public class MainClass {
    public static void Main() {
        string[] stringifiedNums = {"001", "49", "017", "0080", "00027", "2" };
        bool contains = stringifiedNums.Contains("2",new MyStringifiedNumberComparer());
        Console.WriteLine(contains);
    }
}

    

   
 

using System;
using System.Collections.Generic;
using System.Linq;

class LinqDemo {
    static void Main() {
        string[] names = { "J", "P", "G", "Pa" };

        IEnumerable<string> query =
          from n in names
          where n.Contains("a")     
          orderby n.Length          
          select n.ToUpper();       

        foreach (string name in query) Console.Write(name + "/");
    }
}

    

   
 

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;

public class MainClass {
    public static void Main() {
        string[] presidents = {"G", "H", "a", "H", "over", "Jack"};
        int count = presidents.Count();
        Console.WriteLine(count);
    }
}

    

   
 

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;

public class MainClass {
    public static void Main() {
        string[] presidents = {"G", "H", "a", "H", "over", "Jack"};

        int count = presidents.Count(s => s.StartsWith("H"));
        Console.WriteLine(count);

    }
}

    

   
 

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class MainClass {
    public static void Main() {
        string[] presidents = {"ant", "arding", "arrison", "eyes", "over", "ackson"};
        IEnumerable<string> items = presidents.Take(5).Concat(presidents.Skip(5));

        foreach (string item in items)
            Console.WriteLine(item);
    }
}

    

   
 

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class MainClass {
    public static void Main() {
        string[] presidents = {"ant", "arding", "rison", "eyes", "over", "ackson"};
        IEnumerable<string> items = new[] {
                                   presidents.Take(5),
                                   presidents.Skip(5)
                                  }.SelectMany(s => s);
        foreach (string item in items)
            Console.WriteLine(item);
    }
}

    

   
 


using System;
using System.Collections.Generic;
using System.Linq;
public class MainClass {
    public static void Main() {

        int[] seq1 = { 1, 2, 3 };
        int[] seq2 = { 3, 4, 5 };
        IEnumerable<int> concat = seq1.Concat(seq2);    //  { 1, 2, 3, 3, 4, 5 }
        IEnumerable<int> union = seq1.Union(seq2);     //  { 1, 2, 3, 4, 5 }
    }
}