public bool IsNumber(string s) {        int size = s.Length;        if(size == 0) return false;        int numindex = -1;         int dotindex = -1;        int eindex = -1;//e index        var possibleFirstChar = new List<char>(){‘+‘,‘-‘,‘.‘};         var digits = new List<char>(){‘0‘,‘1‘,‘2‘,‘3‘,‘4‘,‘5‘,‘6‘,‘7‘,‘8‘,‘9‘};        if(size == 1 && !digits.Contains(s[0])) return false;        //remove spaces at the beginning till not ‘ ‘        int start = 0;        while(start< size && s[start] == ‘ ‘)        {            start++;        }        if(start == size) return false;        //first letter just        if(!possibleFirstChar.Contains(s[start]) && !digits.Contains(s[start])) return false;        if(possibleFirstChar.Contains(s[start]))        {            if(s[start] == ‘.‘) {                 dotindex = start;            }            start++;        }                             int tempStart = start;        int i =tempStart;        for(;i<size && s[i] != ‘ ‘;i++)        {            if(s[i] == ‘e‘)             {                if(eindex >= 0 || numindex < 0) return false;// cannot have 2 ‘e‘ && must have digits before e                eindex = i;            }            else if(s[i] == ‘.‘)            {                 if(eindex >= 0 || dotindex >= 0) return false; // cannot after ‘2‘ && can not have 2 ‘.‘                 dotindex = i;            }            else if(s[i] == ‘+‘ || s[i] == ‘-‘) //should be just after ‘e‘            {                if( eindex != i-1) return false;            }            else if(!digits.Contains(s[i])) return false;             else numindex = i;        }        //check whether we have extra spaces in the end        if(i != size)        {            while(i<size)            {            if(s[i] !=‘ ‘) return false;            i++;            }        }//blank at end        if((dotindex==0 && eindex == 1)) return false;// such as .e12;        if(numindex < 0 || numindex < eindex) return false;// such as . , e;         return true;    }