2.2 Basic types: Dictionary, C#

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//2.2 Basic types: Dictionary

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

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            //Second most used type is Dictionary
            //Dictionary is a list of Key, Value pairs, where key must be unique
            
            Dictionary<int, string> dic = new Dictionary<int, string>();
            //same as 
            //Dictionary<int, string> dic = new Dictionary<int, string>()
            //{
            //    {5, "five"},
            //    {6, "six"}
            //};

dic[5] = "five"; //O(1) if space need not to be allocated, O(n) otherwise
            dic[6] = "six";
            Console.WriteLine(dic[5]); //O(1)
            
            Console.WriteLine(dic.ContainsKey(6)); //O(1)
            dic.Keys.Where(f => f > 5)
                    .ToList()
                    .ForEach(f => Console.WriteLine(dic[f]+" "));
            //or
            dic.Where(f => f.Key > 5)
               .Select(f => f.Value)
               .ToList()
               .ForEach(f => Console.WriteLine(f + ""));
        }
    }
}

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Compilation time: 0.21 sec, absolute running time: 0.19 sec, cpu time: 0.16 sec, average memory usage: 18 Mb, average nr of threads: 5