using System;

using System.Collections.Generic;

using System.Linq;

​

namespace FindEvenLongestSubString

{

    internal class Program

    {

        static void Main(string[] args)

        {

            string s = "cdbaabaa";

            Console.WriteLine(FindLongestSubString(s));

        }

​

​

        static int FindLongestSubString(string s)

        {

​

            int ans, cur;

            ans = cur = 0;

            var dic = new Dictionary<int, int>() { { 0,-1} };

            foreach (var item in s.Select((value, i) => new { i, value }))

            {

                Console.WriteLine($"i: {item.i}");

                var r = 1 << english.IndexOf(item.value) >> 1;

                Console.WriteLine($"r: {r}");

                cur ^= r;

                Console.WriteLine($"cur: {cur}");

                if (!dic.ContainsKey(cur))

                {

                    dic.Add(cur, item.i);

                }

                ans = Math.Max(item.i - dic[cur], ans);

                Console.WriteLine($"ams: {ans}");

                Console.WriteLine("=======");

            }

            return ans;

        }

​

        const string english = "abcdefghijklmnopqrstuvwxyz";

    }

}