LeetCode OJ：Regular Expression Matching（正则表达式匹配）

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", "c*a*b") → true

正则表达式的匹配，注意*代表的不是任意的字符，而是0个或者任意多个前向的字符，代码如下：

class Solution {
public:
    bool isMatch(string s, string p) {
           if(p.size() == 0) return s.size() == 0;
           if(p[1] != '*'){
               if(s.size() != 0 && (p[0] == s[0] || p[0] == '.')) 
                   return isMatch(s.substr(1), p.substr(1));
               return false;
           }else{
               while(s.size() != 0 &&(s[0] == p[0] || p[0] == '.')){//模式串匹配0个或者更多的字符
                   if(isMatch(s, p.substr(2)))
                       return true;
                   s = s.substr(1);
               }
               return isMatch(s, p.substr(2));
           }
    }
};