面试题31：字符串正则表达式的递归匹配

mplement 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

 1 class Solution {
 2 public:
 3     bool isMatch(const char *s, const char *p) {
 4 
 5         if (*p == '') return *s == '';
 6 
 7         if (*(p + 1) == '*') {
 8             if (*s == *p || *p == '.') {
 9                 if (*s == '') {
10                     return isMatch(s, p + 2);
11                 } else {
12                     return isMatch(s, p + 2) || isMatch(s + 1, p) || isMatch(s + 1, p + 2);
13                 }
14             } else {
15                 return isMatch(s, p + 2);
16             }
17         }
18         if (*s == *p || (*p == '.' && *s != '')) {
19             return isMatch(s + 1, p + 1);
20         }
21         return false;
22     }
23 };