//First, Last, Single, and ElementAt

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

        int[] numbers = { 10, 9, 8, 7, 6 };
        int firstNumber = numbers.First();    
        int lastNumber = numbers.Last();      
        int secondNumber = numbers.ElementAt(1);
        int lowestNumber = numbers.OrderBy(n => n).First();
    }
}

    

   
 

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

public class MainClass{
   public static void Main(){
            int[] numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9};
            var query = numbers.ElementAt(4);
            Console.Write(query);
   }
}

    

   
 

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

public class Tree<TreeNode> : IEnumerable<TreeNode> where TreeNode : IComparable<TreeNode> {
    public Tree(TreeNode nodeValue) {
        this.NodeData = nodeValue;
        this.LeftTree = null;
        this.RightTree = null;
    }

    public void Insert(TreeNode newItem) {
        TreeNode currentNodeValue = this.NodeData;
        if (currentNodeValue.CompareTo(newItem) > 0) {
            if (this.LeftTree == null) {
                this.LeftTree = new Tree<TreeNode>(newItem);
            } else {
                this.LeftTree.Insert(newItem);
            }
        } else {
            if (this.RightTree == null) {
                this.RightTree = new Tree<TreeNode>(newItem);
            } else {
                this.RightTree.Insert(newItem);
            }
        }
    }

    public void WalkTree() {
        if (this.LeftTree != null) {
            this.LeftTree.WalkTree();
        }

        Console.WriteLine(this.NodeData.ToString());

        if (this.RightTree != null) {
            this.RightTree.WalkTree();
        }
    }

    public TreeNode NodeData { get; set; }
    public Tree<TreeNode> LeftTree { get; set; }
    public Tree<TreeNode> RightTree { get; set; }


    IEnumerator<TreeNode> IEnumerable<TreeNode>.GetEnumerator() {
        if (this.LeftTree != null) {
            foreach (TreeNode item in this.LeftTree) {
                yield return item;
            }
        }

        yield return this.NodeData;

        if (this.RightTree != null) {
            foreach (TreeNode item in this.RightTree) {
                yield return item;
            }
        }
    }
    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
        throw new NotImplementedException();
    }
}

class Employee : IComparable<Employee> {
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Department { get; set; }
    public int Id { get; set; }

    public override string ToString() {
        return String.Format("Id: {0}, Name: {1} {2}, Dept: {3}", this.Id, this.FirstName, this.LastName, this.Department);
    }
    int IComparable<Employee>.CompareTo(Employee other) {
        if (other == null)
            return 1;

        if (this.Id > other.Id)
            return 1;

        if (this.Id < other.Id)
            return -1;

        return 0;
    }
}

class Program {
    static void Main() {
        Tree<Employee> empTree = new Tree<Employee>(new Employee { Id = 1, FirstName = "Janet", LastName = "Gates", Department = "IT" });
        empTree.Insert(new Employee { Id = 2, FirstName = "O", LastName = "G", Department = "Marketing" });
        empTree.Insert(new Employee { Id = 4, FirstName = "K", LastName = "H", Department = "IT" });
        empTree.Insert(new Employee { Id = 6, FirstName = "L", LastName = "H", Department = "Sales" });
        empTree.Insert(new Employee { Id = 3, FirstName = "E", LastName = "L", Department = "Sales" });
        empTree.Insert(new Employee { Id = 5, FirstName = "D", LastName = "L", Department = "Marketing" });

        var depts = (from d in empTree select d.Department).Distinct();

        foreach (var dept in depts)
            Console.WriteLine("Department: {0}", dept);
    }
}

    

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

public class MainClass {
    public static void Main() {
        string[] presidents = {"Grant", "Harding", "Harrison", "Hayes", "Hoover", "Jackson"};
        Console.WriteLine("presidents count:  " + presidents.Count());
        IEnumerable<string> presidentsWithDupes = presidents.Concat(presidents);
        Console.WriteLine("presidentsWithDupes count:  " + presidentsWithDupes.Count());
        IEnumerable<string> presidentsDistinct = presidentsWithDupes.Distinct();
        Console.WriteLine("presidentsDistinct count:  " + presidentsDistinct.Count());
    }
}

    

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

public class MainClass {
public static void Main() {

List products = GetProductList(); var categoryNames = (
from p in products
select p.Category)
.Distinct();

Console.WriteLine(“Category names:”);
foreach (var n in categoryNames) {
Console.WriteLine(n);
}
}
static List GetProductList() {
List empTree = new List();
empTree.Add(new Product { ProductName = “A”, Category = “O”, UnitPrice = 12, UnitsInStock = 5, Total = 36, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = “B”, Category = “O”, UnitPrice = 2, UnitsInStock = 4, Total = 35, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = “C”, Category = “O”, UnitPrice = 112, UnitsInStock = 3, Total = 34, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = “D”, Category = “O”, UnitPrice = 112, UnitsInStock = 0, Total = 33, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = “E”, Category = “O”, UnitPrice = 1112, UnitsInStock = 2, Total = 32, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = “F”, Category = “O”, UnitPrice = 11112, UnitsInStock = 0, Total = 31, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
return empTree;
}
}
class Product : IComparable {
public string ProductName { get; set; }
public string Category { get; set; }
public int UnitPrice { get; set; }
public int UnitsInStock { get; set; }
public int Total { get; set; }
public DateTime OrderDate { get; set; }
public int Id { get; set; }

public override string ToString() {
return String.Format(“Id: {0}, Name: {1} , Category: {3}”, this.Id, this.ProductName, this.Category);
}
int IComparable.CompareTo(Product other) {
if (other == null)
return 1;
if (this.Id > other.Id)
return 1;

if (this.Id < other.Id) return -1; return 0; } } [/csharp]

   
 

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

public class MainClass {
    public static void Main() {

        int[] fl = { 2, 2, 3, 5, 5 };

        var uniqueFactors = fl.Distinct();

        Console.WriteLine("Prime factors of 300:");
        foreach (var f in uniqueFactors) {
            Console.WriteLine(f);
        }
    }
}

    

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

public class MainClass{
   public static void Main(){
            int[] numbers = {1, 1, 2, 3, 3};
            Console.Write(numbers.Distinct());
   }
}