CODEWITHSUNDEEP
c#algorithmrecursion
sapbucket
sapbucket

Reputation: 7195

Recursive dealing of cards from deck?

A standard 52 card deck may be represented using integer values: {0,1,..,50,51}. A standard poker hand contains 5 values from this set, without repetition.

To represent all 52C5 unique hands from a deck, the following loop may be used:

    for (int card1 = 0; card1 < 48; card1++)
    {
        for (int card2 = card1 + 1; card2 < 49; card2++)
        {
            for (int card3 = card2 + 1; card3 < 50; card3++)
            {
                for (int card4 = card3 + 1; card4 < 51; card4++)
                {
                    for (int card5 = card4 + 1; card5 < 52; card5++)
                    {
                        var handAbcde = new List<int> { card1, card2, card3, card4, card5 };
                        // do something with the hand...
                    }
                }
            }
        }
    }

I would like to know how to make this a recursive function. I attempted but I could not preserve the ordering of the cards from lowest to highest, as it would for the for loops above.

Example of desired output: (observe sequential ordering from lowest to highest without repetition)

0 1 2 3 4
0 1 2 3 5
0 1 2 3 6
.
.
.
47 48 49 50 49
47 48 49 50 50
47 48 49 50 51

Upvotes: 0

Views: 571

Answers (1)

leviathanbadger
leviathanbadger

Reputation: 1712

Here's a helpful extension method, which does what you want using recursion:

public static IEnumerable<IEnumerable<T>> GetPermutations<T>(this IEnumerable<T> items, int count)
{
    int i = 0;
    foreach (var item in items)
    {
        if (count == 1) yield return new T[] { item };
        else foreach (var result in items.Skip(i + 1).GetPermutations(count - 1))
            yield return new T[] { item }.Concat(result);
        ++i;
    }
}

And here's a sample use, to generate all possible combinations of five cards from a 52-card deck:

foreach (var hand in Enumerable.Range(0, 52).GetPermutations(5))
{
    foreach (var card in hand)
        Console.Write(card + " ");
    Console.WriteLine();
}

Upvotes: 3

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