Find the longest non-repeating substring of a string, output the largest substring

For example: Ababcdebc, so his biggest substring is: ABCDE

Using system;using system.collections.generic;using system.linq;using system.text;using  system.threading.tasks;namespace consoleapplication4{    class program{         static void main (String[] args) {             string s =  "ABCABABCDEFGFG";             char[] list = s.tochararray () ;             findmaxsubdifferencestring ss  = new findmaxsubdifferencestring (); SS. Findmaxsubdifferencestrings (list, s.length);             string s1 =  "AAAAAA";             char[] list1 = s1. ToCharArray (); SS. FindmaxsubdifferenceStringS (list1, s1. Length);            string s2 =  " Ababab ";            char[] list2 =  S2. ToCharArray (); SS. Findmaxsubdifferencestrings (LIST2,&NBSP;S2. Length);            string s3 =  " ABCABABCDEFGFGABCABABCDEFGFG ";             char[]  list3 = s3. ToCharArray (); SS. Findmaxsubdifferencestrings (LIST3,&NBSP;S3.　Length);}}     public class FindMaxSubDifferenceString{         public bool isdup (char[] list, int len, char targetchar,  Int begin, int end, out int targetindex) {targetindex = -1;             // note: first, we need to check all parameters are  Valid, such as list is null, len >0, or begin <end,  begin>0, end<len, etc             for (int i=begin;i<=end; i++) {                 if (List[i]==targetchar) {targetindex = i;                     return 　true;}}             return false;}         public void findmaxsubdifferencestrings (char[]  List, int len) {            if  (list  == null)  return;            if  (len <= 0)  return;            int maxsubstringlen  = 0;            int  maxsubstringbeginindex = 0;             int currentmaxsubstringbeginindex = 0;             int currentMaxSubLen = 0;             for  (int i = 1; i < len; i++) {                 int dupindex =  -1;                if   (Isdup (LIST,&NBSP;LEN,&NBSP;LIST[I],&NBsp;currentmaxsubstringbeginindex, i - 1, out dupindex)) {currentMaxSubLen =  i - currentMaxSubStringBeginIndex;                     if  (currentmaxsublen >  Maxsubstringlen) {maxsubstringlen = currentmaxsublen;maxsubstringbeginindex =  Currentmaxsubstringbeginindex;}                      else{}currentmaxsubstringbeginindex = dupindex + 1;}                 else // not dup{}}             if  ( maxsubstringlen == 0) {Maxsubstringlen = len;}             console.write ("INPUT&Nbsp;string:  ");            for  (int  i = 0; i < len; i++) {                 console.write (List[i]);}             console.writeline ("");             console.write ("after input: ");             for  (int i =  maxsubstringbeginindex; i < maxsubstringbeginindex + maxsubstringlen; i++) {                 console.write ( List[i]);}　             console.writeline ("");}}

Find the longest non-repeating substring of a string, output the largest substring