Check Half-Width String and convert 3, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using System.Text;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            //Your code goes here
            Console.WriteLine("ﾁﾖﾁﾖﾁ");
            Console.WriteLine("ﾁﾖﾁﾖﾁ".Normalize(NormalizationForm.FormKC));
            Console.WriteLine("チヨチヨチ");
            Console.WriteLine("チヨチヨチ".Normalize(NormalizationForm.FormKC));

Console.WriteLine(FullWidthCharactersHandler.isHalfWidthString("チヨチヨチ"));
            Console.WriteLine(FullWidthCharactersHandler.isHalfWidthString("ﾁﾖﾁﾖﾁ"));
            Console.WriteLine(FullWidthCharactersHandler.isHalfWidthString("ﾁﾖﾁﾖﾁヨチ"));

Console.WriteLine(FullWidthCharactersHandler.convertFullWidthToHalfWidth("チヨチヨチ"));
            Console.WriteLine(FullWidthCharactersHandler.convertFullWidthToHalfWidth("ﾁﾖﾁﾖﾁ"));
            Console.WriteLine(FullWidthCharactersHandler.convertFullWidthToHalfWidth("ﾁﾖﾁﾖﾁヨチ"));

}
    }
    public class FullWidthCharactersHandler
    {

static Dictionary<char, char> fullWidth2halfWidthDic;
        static FullWidthCharactersHandler()
        {
            fullWidth2halfWidthDic = new Dictionary<char, char>();
            string fullWidthChars = "アイウエオカキクケコサシスセソタチツテトナニヌネノハヒフヘホマミムメモヤユヨラリルレロワヲンッァィゥェォャュョ゙゚ー０１２３４５６７８９ＡＢＣＤＥＦＧＨＩＪＫＬＭＮＯＰＱＲＳＴＵＶＷＸＹＺａｂｃｄｅｆｇｈｉｊｋｌｍｎｏｐｑｒｓｔｕｖｗｘｙｚ";
            string halfWidthChars = "ｱｲｳｴｵｶｷｸｹｺｻｼｽｾｿﾀﾁﾂﾃﾄﾅﾆﾇﾈﾉﾊﾋﾌﾍﾎﾏﾐﾑﾒﾓﾔﾕﾖﾗﾘﾙﾚﾛﾜｦﾝｯｧｨｩｪｫｬｭｮﾞﾟｰ0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
            for (int i = 0; i < fullWidthChars.Length; i++)
            {
                fullWidth2halfWidthDic.Add(fullWidthChars[i], halfWidthChars[i]);
            }
        }

public static bool isHalfWidthString(string toTestString)
        {
            bool isHalfWidth = true;
            foreach (char ch in toTestString)
            {
                if (fullWidth2halfWidthDic.ContainsKey(ch))
                {
                    isHalfWidth = false;
                    break;
                }
            }
            return isHalfWidth;
        }

public static string convertFullWidthToHalfWidth(string theString)
        {
            StringBuilder sbResult = new StringBuilder(theString);
            for (int i = 0; i < theString.Length; i++)
            {
                if (fullWidth2halfWidthDic.ContainsKey(theString[i]))
                {
                    sbResult[i] = fullWidth2halfWidthDic[theString[i]];
                }
            }
            return sbResult.ToString();
        }
    }
}

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Compilation time: 0,14 sec, absolute running time: 0,13 sec, cpu time: 0,12 sec, average memory usage: 14 Mb, average nr of threads: 3, absolute service time: 0,3 sec