How to write an anagram generator in pure C# and .Net framework [closed]

Question

I would like to generate anagram output of a given string without the help of any external libraries such as Google anagram algorithms helper.

Example:

Input string = "GOD"

Output list should look like the following one:

G O D GO GD OD OG DG DO GOD GDO ODG OGD DGO DOG

Answer 1

That taks turned to be awesome on so many levels. I present you a pure LINQ (but not very efficient) solution.

    static class Program
    {
        static void Main(string[] args)
        {
            var res = "cat".Anagrams();

            foreach (var anagram in res)
                Console.WriteLine(anagram.MergeToStr());
        }

        static IEnumerable<IEnumerable<T>> Anagrams<T>(this IEnumerable<T> collection) where T: IComparable<T>
        {
            var total = collection.Count();

            // provided str "cat" get all subsets c, a, ca, at, etc (really nonefficient)
            var subsets = collection.Permutations()
                .SelectMany(c => Enumerable.Range(1, total).Select(i => c.Take(i)))
                .Distinct(new CollectionComparer<T>());

            return subsets;
        }

        public static IEnumerable<IEnumerable<T>> Permutations<T>(this IEnumerable<T> collection)
        {
            return collection.Count() > 1 
                ?
                    from ch in collection
                    let set = new[] { ch }
                    from permutation in collection.Except(set).Permutations()
                    select set.Union(permutation)
                :
                    new[] { collection };
        }

        public static string MergeToStr(this IEnumerable<char> chars)
        {
            return new string(chars.ToArray());
        }

    }// class

    // cause Distinct implementation is shit
    public class CollectionComparer<T> : IEqualityComparer<IEnumerable<T>> where T: IComparable<T>
    {
        Dictionary<IEnumerable<T>, int> dict = new Dictionary<IEnumerable<T>, int>();

        public bool Equals(IEnumerable<T> x, IEnumerable<T> y)
        {
            if (x.Count() != y.Count())
                return false;
            return x.Zip(y, (xi, yi) => xi.Equals(yi)).All(compareResult => compareResult);
        }

        public int GetHashCode(IEnumerable<T> obj)
        {
            var inDict = dict.Keys.FirstOrDefault(k => Equals(k, obj));
            if (inDict != null)
                return dict[inDict];
            else
            {
                int n = dict.Count;
                dict[obj] = n;
                return n;
            }
        }
    }// class