Permutation.cs

using System.Collections.Generic;
using System.Linq;

namespace Algorithms.Strings
{
    public static class Permutation
    {
        /// <summary>
        /// Returns every anagram of a given word.
        /// </summary>
        /// <returns>List of anagrams.</returns>
        public static List<string> GetEveryUniquePermutation(string word)
        {
            if (word.Length < 2)
            {
                return new List<string>
                {
                    word,
                };
            }

            var result = new HashSet<string>();

            for (var i = 0; i < word.Length; i++)
            {
                var temp = GetEveryUniquePermutation(word.Remove(i, 1));

                result.UnionWith(temp.Select(subPerm => word[i] + subPerm));
            }

            return result.ToList();
        }
    }
}