class Solution {

public:

    /**

     * @param s the string that represents a number

     * @return whether the string is a valid number

     */

    bool isNumber(string& s) {

        bool num = false, numAfterE = true, dot = false, exp = false, sign = false;

        int n = s.size();

        for (int i = ; i < n; ++i) {

            if (s[i] == ' ') {

                if (i < n -  && s[i + ] != ' ' && (num || dot || exp || sign)) return false;

            } else if (s[i] == '+' || s[i] == '-') {

                if (i >  && s[i - ] != 'e' && s[i - ] != ' ') return false;

                sign = true;

            } else if (s[i] >= '' && s[i] <= '') {

                num = true;

                numAfterE = true;

            } else if (s[i] == '.') {

                if (dot || exp) return false;

                dot = true;

            } else if (s[i] == 'e') {

                if (exp || !num) return false;

                exp = true;

                numAfterE = false;

            } else return false;

        }

        return num && numAfterE;

    }

};