FSM

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

namespace FSM
{
    class Program
    {
        enum State
        {
            EMPTY, N, NA, NAN, NANO
        }

        static bool ContainsNano(string text)
        {
            State state = State.EMPTY;
            foreach (var sym in text)
            {
                switch (state)
                {
                    case State.EMPTY:
                        if (sym == 'n')
                        {
                            state = State.N;
                        }
                        break;
                    case State.N:
                        if (sym == 'a')
                        {
                            state = State.NA;
                        }
                        else if (sym == 'n')
                        {
                            // same state
                        }
                        else
                        {
                            state = State.EMPTY;
                        }
                        break;
                    case State.NA:
                        if (sym == 'n')
                        {
                            state = State.NAN;
                        }
                        else
                        {
                            state = State.EMPTY;
                        }
                        break;
                    case State.NAN:
                        if (sym == 'n')
                        {
                            state = State.N;
                        }
                        else if (sym == 'o')
                        {
                            return true;
                           // state = State.NANO;
                        }
                        else if (sym == 'a')
                        {
                            state = State.NA;
                        }
                        else
                        {
                            state = State.EMPTY;
                        }
                        break;
                }
            }
            return false;
        }

        static int CountNano(string text)
        {
            int cnt = 0;
            State state = State.EMPTY;
            foreach (var sym in text)
            {
                switch (state)
                {
                    case State.EMPTY:
                        if (sym == 'n')
                        {
                            state = State.N;
                        }
                        break;
                    case State.N:
                        if (sym == 'a')
                        {
                            state = State.NA;
                        }
                        else if (sym == 'n')
                        {
                            // same state
                        }
                        else
                        {
                            state = State.EMPTY;
                        }
                        break;
                    case State.NA:
                        if (sym == 'n')
                        {
                            state = State.NAN;
                        }
                        else
                        {
                            state = State.EMPTY;
                        }
                        break;
                    case State.NAN:
                        if (sym == 'n')
                        {
                            state = State.N;
                        }
                        else if (sym == 'o')
                        {
                            cnt++;
                            state = State.NANO;
                        }
                        else if (sym == 'a')
                        {
                            state = State.NA;
                        }
                        else
                        {
                            state = State.EMPTY;
                        }
                        break;
                    case State.NANO:
                        if (sym == 'n')
                        {
                            state = State.N;
                        }
                        else
                        {
                           state = State.EMPTY;
                        }
                        break;
                }
            }
            return cnt;
        }
        static void Main(string[] args)
        {
            Console.WriteLine(CountNano("nanonanonano"));
        }
    }
}