using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        string sample = "code project";

​

        var letterCounter = sample.Where(char.IsLetterOrDigit)

                                  .GroupBy(char.ToLower)

                                  .Select(counter => new { Letter = counter.Key, Counter = counter.Count() });

​

        foreach (var counter in letterCounter)

        {

            Console.WriteLine(String.Format("{0} = {1}", counter.Letter, counter.Counter));

        }   

        //int[] numbers = Enumerable.Range(1, 100000).ToArray();

        int[] numbers = {1, 2,1,100,3};

        Console.WriteLine(Fun(numbers));

        Console.WriteLine(solution2(numbers));

        Console.WriteLine(solution(numbers));

    }

    public static int recFind(int[] a, int b) {

        //must be > 0

        if (b <= 0) {

            b = 1;

        }

        int nextMin = b;

        //return the number if >0 and not in array

        if (b > 0 && !a.Any(i=> i == b)) {

            return b;

        }

        nextMin++;

        //else recursive call

        return recFind(a, nextMin);

    }

    public static int solution(int[] a) {

        //find the min

        int min = 1;

        if (a.Length == 0) {

            return min;

        }

        foreach(int i in a.OrderBy(x=>x)) {

            if (i == min) {

                min++;  

            }

        }

        return min;

    }

    public static int Fun(int[] A) {

        // the minimum possible answer is 1

        int result = 1; 

        // let's keep track of what we find

        Dictionary<int,bool> found = new Dictionary<int,bool>();

​

        // loop through the given array  

        for(int i=0;i<A.Length;i++) {

            // if we have a positive integer that we haven't found before

            if(A[i] > 0 && !found.ContainsKey(A[i])) {

                // record the fact that we found it

                found.Add(A[i], true);

            }

        }

​

        // crawl through what we found starting at 1

        while(found.ContainsKey(result)) {

            // look for the next number

            result++;

        }

​

        // return the smallest positive number that we couldn't find.

        return result;

    }

    public static int solution2(int[] A)

    {

        int flag = 1;

​

        A = A.OrderBy(x => x).ToArray();

​

        for (int i = 0; i < A.Length; i++)

        {

            if (A[i] <= 0)

                continue;

            else if (A[i] == flag)

            {

                flag++;

            }

​

        }

​

        return flag;

    }

}