Checks if a string is a permutation of a palindrome. Solution-idea from https://medium.com/algorithms-practice/given-a-string-check-if-it-is-a-permutation-of-a-palindrome-e0469f47761d

IsPermutationOfPalindrome.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace PermutationOfPalindrome
{
    class Program
    {
        static void Main(string[] args)
        {
            IPermutationPalindromeChecker checker = new PermutationPalindromeCheckerImpl();
            PrintCheckerResult(checker, "ned den laks skal"); // True (den laks skal ned)
            PrintCheckerResult(checker, "ned den laks Skal"); // False (because of capitalized S)
            PrintCheckerResult(checker, "1122443553"); // True (1234554321)
            PrintCheckerResult(checker, "112244353"); // True (123454321)
            PrintCheckerResult(checker, "Hej"); // False
        }

        private static void PrintCheckerResult(IPermutationPalindromeChecker checker, string s)
        {
            Console.WriteLine(s + " " + checker.IsPermutationOfPalindrome(s));
        }
    }

    interface IPermutationPalindromeChecker
    {
        bool IsPermutationOfPalindrome(string s);
    }

    class PermutationPalindromeCheckerImpl : IPermutationPalindromeChecker
    {
        private static Dictionary<char, int> charsUsed;
        public bool IsPermutationOfPalindrome(string s)
        {
            charsUsed = new Dictionary<char, int>();
            foreach (var c in s)
            {
                charsUsed[c] = charsUsed.ContainsKey(c) ? charsUsed[c] + 1 : 1;
            }

            return charsUsed.Where(e => e.Value % 2 != 0).Count() <= 1;
        }
    }
}