Leetcode: Regular Expression Matching

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

貌似简单，实现起来相当的不容易，主要是*的处理，greedy方法不行，需要backtrack。讨论区的实现。。。

class Solution {
public:
bool isMatch(const char *s, const char *p) {
assert(s && p);
if (*p == 0) {
return (*s == 0);
}

if (*(p+1) != '*') {
return (*p == *s || *p == '.' && *s != 0) && isMatch(s+1, p+1);
}

while (*p == *s || *p == '.' && *s != 0) {
if (isMatch(s, p+2)) {
return true;
}
++s;
}

return isMatch(s, p+2);
}
};