using System;

using System.Linq;

using System.Text;

using System.Collections.Generic;

​

public class record

{

    public int flashid { get; set; }

    public int position { get; set; }

    public string value { get; set; }

}      

​

public class Program

{

    static void Recursive(record record, List<string> bag, Stack<record> stack, List<record> list)

    {

        stack.Push(record);

        if (record.position == 10)

        {

            var temp = new StringBuilder();

            foreach (var item in stack)                

                temp.Insert(0, item.value);

            bag.Add(temp.ToString());                

        }

        else            

            foreach (var item in list.Where(x => x.position == record.position + 1))                

                Recursive(item, bag, stack, list);                            

        stack.Pop();            

    }

    static List<string> Solve(List<record> list)

    {

        for (var i = 1; i <= 10; i++)

            if (!list.Any(x => x.position == i))

                list.Add(new record { position = i, value = "." });

        var bag = new List<string>();

        var stack = new Stack<record>();

        foreach (var record in list.Where(x => x.position == 1))

            Recursive(record, bag, stack, list);

        return bag;

    }

    public static void Main()

    {

        var list = new List<record>

        {

            new record{ flashid = 450, position = 5, value = "a"},

            new record{ flashid = 450, position = 6, value = "b"},

            new record{ flashid = 450, position = 7, value = "c"},

            new record{ flashid = 450, position = 7, value = "d"},

            new record{ flashid = 450, position = 7, value = "e"},

            new record{ flashid = 450, position = 8, value = "f"},          

            new record{ flashid = 450, position = 9, value = "g"}

        };

        var answer = Solve(list);       

        Console.WriteLine("[" + string.Join(", ", answer) + "]"); 

    }

}