Family Gift Exchange Program

Program.cs

//everybody to give/recieve a gift
List<string> players = new List<string> { "Peter", "Emma", "John", "Chris", "Patty", "Karen", "Jenny", "Sloane" };
players.Sort();

Dictionary<string,List<string>> restrictions = new Dictionary<string,List<string>>();

// Rule:  players can't give to themselves
players.ForEach(p => restrictions.Add(p, new List<string> { p }));

// Rule: players can't give to their partner
restrictions["Peter"].Add("Emma");
restrictions["Emma"].Add("Peter");
restrictions["John"].Add("Chris");
restrictions["Chris"].Add("John");
restrictions["Jenny"].Add("Sloane");

// exchanges from last year
// tracked to ensure no repeat giving
var lastYear= new Dictionary<string, string>()
{
    {"Emma", "John" },
    {"Peter", "Karen" },
    {"Karen", "Jenny" },
    {"John", "Sloane" },
    {"Chris", "Emma" },
    {"Jenny", "Chris" },
    {"Sloane", "Chris" },
    {"Patty", "Peter" }
};

//using a seed that makes drawings repeatable
Random random = new Random(1);

Dictionary<string, string> draw(Dictionary<string, string> previous)
{
    bool failed;
    var result = new Dictionary<string, string>();
    var chosen = new HashSet<string>();
    do        
    {        
        failed = false;
        foreach (var giver in players)
        {
            List<string> validChoices = new List<string>();
            validChoices.AddRange(players.Where(p => !restrictions[giver].Contains(p) && previous[giver] != p && !chosen.Contains(p)));
            if (validChoices.Count == 0)
            {
                failed = true;
                result.Clear();
                chosen.Clear();
                break;
            }
            string recipient = validChoices.ElementAt(random.Next(validChoices.Count));
            result[giver] = recipient;
            chosen.Add(recipient);
        }        
    }
    while (failed);
    return result;
}

int year = 2021;
var exchanges = new Dictionary<int, Dictionary<string, string>>();
while (year <= 2030)
{   
    exchanges.Add(year, lastYear);
    lastYear = draw(lastYear);
    year++;
}

Console.WriteLine($"YEAR,{string.Join(",", players.Select(p=>p.ToUpper()))}");
foreach (int y in exchanges.Keys.OrderBy(x=>x))
{
    var map = exchanges[y];
    string recipients = string.Join(",", players.Select(p => map[p]));
    Console.WriteLine($"{y},{recipients}");
}