65

class Solution {
public:
    bool isNumber(string s) {
        bool seenDigit = false;
        bool seenExpo = false;
        bool seenDot = false;

        for(int i=0; i<s.length(); i++){
            char ch = s[i];
            if(isdigit(ch)){
                seenDigit = true;
            }
            else if(ch == '+' || ch == '-'){
                if(i > 0 && s[i-1] != 'e' && s[i-1] != 'E'){
                    return false;
                }
            }
            else if(ch == 'e' || ch == 'E'){
                if(seenExpo || !seenDigit){
                    return false;
                }
                seenExpo = true;
                seenDigit = false;
            }
            else if(ch == '.'){
                if(seenExpo || seenDot)
                    return false;
                seenDot = true;
            }
            else{
                return false;
            }
        }
        return seenDigit;
    }
};