leetcode 65

看到这题果断看答案学习一波。。感觉没啥用

正则表达式：

#include <string>
#include <regex>

class Solution {
private:
    static std::regex const number_pattern;
public:
    bool isNumber(std::string const& s) {
        return std::regex_match(s, number_pattern);
    }
};

// non-(const integral) static member variables must be initialized out-of-line.
std::regex const Solution::number_pattern{R"(^\s*[-+]?(?:\d+|\d+\.\d*|\d*\.\d+)(?:e[+-]?\d+)?\s*$)"};