public class Solution {

    public bool IsIsomorphic(string s, string t) {

        if (s.Length != t.Length)

            {

                return false;

            }

            else

            {

                Dictionary<char, int> dic1 = new Dictionary<char, int>();

                Dictionary<char, int> dic2 = new Dictionary<char, int>();

                int type1 = ;

                int type2 = ;

                StringBuilder sb1 = new StringBuilder();

                StringBuilder sb2 = new StringBuilder();

                foreach (var c in s)

                {

                    if (!dic1.ContainsKey(c))

                    {

                        dic1.Add(c, type1);

                        sb1.Append(type1);

                        type1++;

                    }

                    else

                    {

                        sb1.Append(dic1[c]);

                    }

                }

                foreach (var c in t)

                {

                    if (!dic2.ContainsKey(c))

                    {

                        dic2.Add(c, type2);

                        sb2.Append(type2);

                        type2++;

                    }

                    else

                    {

                        sb2.Append(dic2[c]);

                    }

                }

                if (sb1.ToString() != sb2.ToString())

                {

                    return false;

                }

                else

                {

                    return true;

                }

            }

    }

}