LeetCode[String]: Valid Number

Validate if a given string is numeric.
Some examples:
"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true
Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.

这个题目是我在LeetCode上遇到的最闹心的题目，这个题目没有给出合法数字的定义，我们要做的就是不断地测试，直到处理所有的情况为止。

我的C++代码如下：

    bool isNumber(string s) {
        s.erase(0, s.find_first_not_of(" "));
        s.erase(s.find_last_not_of(" ") + 1);
        s.erase(0, s.find_first_not_of("+"));
        s.erase(0, s.find_first_not_of("-"));

        if (s[0] == ‘e‘ || s[s.size() - 1] == ‘e‘) return false;
        if (s[0] == ‘.‘ && s[1] == ‘e‘) return false;

        bool isFloat = false;
        bool isScientific = false;
        bool lastIsE = false;
        for (auto c : s) {
            if (lastIsE) {
                lastIsE = false;
                if (c != ‘+‘ && c != ‘-‘ && (c < ‘0‘ || c > ‘9‘)) return false;
            }
            else if (c == ‘.‘) {
                if (isFloat || isScientific) return false;
                isFloat = true;
            }
            else if (c == ‘e‘) {
                if (isScientific) return false;
                isScientific = true;
                lastIsE = true;
            }
            else if (c < ‘0‘ || c > ‘9‘)
                return false;
        }

        if (s[s.size() - 1] == ‘+‘ || s[s.size() - 1] == ‘-‘) return false;
        if (s.size() == 1 && (isFloat || isScientific)) return false;
        return s.empty() ? false : true;
    }

时间性能如下图所示：