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

此题主要是 * 需要特殊处理。

它既能使其前驱字符匹配多个，同时也能匹配0个字符。

class Solution {
public:
   bool isMatch(const char *s, const char *p) {

        if (!*p) return !*s;

        if (*(p+1) == '*') {
                while (*s) {
                        if (isMatch(s, p+2))
                                return true;

                        if (*p == *s || *p =='.') {
                                ++s;
                        }
                        else {
                                return false;
                        }
                }

                return isMatch(s, p+2);
        }
        else if (*s == *p || (*s && *p == '.'))
                return isMatch(++s, ++p);
        else
                return false;
   }
};

Regular Expression Matching -- leetcode