正则式匹配

Implement regular expression matching with support for '.' and '*'.

'.' Matches any single character.
'*' Matches zero or more of the preceding element.

The matching should cover the entire input string (not partial).

The function prototype should be:
bool isMatch(const char *s, const char *p)

Some examples:
isMatch("aa","a") → false
isMatch("aa","aa") → true
isMatch("aaa","aa") → false
isMatch("aa", "a") → true
isMatch("aa", ".") → true
isMatch("ab", ".") → true
isMatch("aab", "ca*b") → true

递归解法
#include <string>
using std::string;

class Solution {
public:
    bool isMatch(string s, string p) {
        if(p.empty()) return s.empty();
        
        if(p.size()<2)
            return !s.empty() && s.size() < 2 && (p[0] == s[0] || p[0] == '.');
        
        if(p[1] == '*')
            return isMatch(s, p.substr(2)) || !s.empty() && ((s[0] == p[0] || p[0] == '.') && isMatch(s.substr(1), p));
        else
            return !s.empty() && (s[0] == p[0] || p[0] == '.') && isMatch(s.substr(1), p.substr(1));
    }
};