using System;
using System.Collections.Generic;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            char[] arr = { 'a', 'b', 'c' };

            List<string> result = getCombinations(arr);

            // Show result
            foreach (var item in result)
            {
                Console.WriteLine(item);
            }

            // Delay
            Console.ReadKey();
        }

        public static List<string> getCombinations(char[] arr)
        {
            List<string> resultList = new List<string>();
            string sStringResult1;
            string sStringResult2;

            for (int ix = 0; ix < arr.Length; ix++)
            {
                for (int iy = 0; iy < arr.Length; iy++)
                {
                    for (int iz = 0; iz < arr.Length; iz++)
                    {
                        if (ix == iy) { continue; }
                        if (ix == iz) { continue; }
                        if (iy == iz) { continue; }

                        sStringResult1 = arr[ix].ToString() + arr[iy].ToString() + arr[iz].ToString();
                        resultList.Add(sStringResult1);

                        sStringResult2 = arr[iy].ToString() + arr[iz].ToString();
                        resultList.Add(sStringResult2);
                    }
                }
            }

            foreach (var item in arr)
            {
                resultList.Add(item.ToString());
            }

            return resultList;
        }
    }
}