剑指OFFER----面试题20. 表示数值的字符串

class Solution {
public:
    bool isNumber(string s) {
        if (s.empty()) return false;
        bool e = 0, dot = 0, num = 0;
        int lo = 0, hi = s.size() - 1;
        while (lo <= hi && s[lo] == ‘ ‘) lo++;
        while (lo <= hi && s[hi] == ‘ ‘) hi--;
        if (lo > hi) return false;
        lo += (s[lo] == ‘+‘ || s[lo] == ‘-‘);

        for (int i = lo; i <= hi; ++i) {
            if (s[i] >= ‘0‘ && s[i] <= ‘9‘) num = 1;
            else if (s[i] == ‘.‘) {
                if (dot || e) return false;
                dot = 1;
            } else if(s[i] == ‘e‘) {
                if (e || !num || i == hi) return false;
                if (s[i + 1] == ‘+‘ || s[i  + 1] == ‘-‘) ++i;
                e = 1, num = 0;
            } else return false;
        }
        return num;
    }
};