c# - Words combinations without repetition

Question

I have 10 words. How can I get all possible combinations of 5 words (n=10, k=5). The order does not matter.

For example: "A", "B", "C", if k=2 (n=3 in this case), it would like AB, BC and AC. Maybe you know some usefull code or example.

P.S. Sorry if I'm not right enough cause I don't know English very good.

Answer 1

What you are trying to do is get all the permutations of a collection.

• Unique permutations of list
• permutations of k objects from a set of n algorithm

Here is the code snippet:

static void Main(string[] args)
{
    var list = new List<string> { "a", "b", "c", "d", "e" };
    var result = GetPermutations(list, 3);
    foreach (var perm in result)
    {
        foreach (var c in perm)
        {
            Console.Write(c + " ");
        }
        Console.WriteLine();
    }
    Console.ReadKey();
}

static IEnumerable<IEnumerable<T>> GetPermutations<T>(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 GetPermutations(items.Skip(i + 1), count - 1))
                yield return new T[] { item }.Concat(result);
        }

        ++i;
    }
}

Outputs:

a b c 
a b d 
a b e 
a c d 
a c e 
a d e 
b c d 
b c e 
b d e 
c d e