leetcode: Regular Expression Matching

http://oj.leetcode.com/problems/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

思路：

关键在于'*'的处理。对于类似于"a*"的情况，我们可以匹配0个'a'，也可以匹配尽可能多的'a'。

class Solution {
public:
    bool isMatch(const char *s, const char *p) {
        if ('\0' == *p) { 
            return '\0' == *s;
        }
        
        if ('*' == *(p + 1)) {
            while ((*s != '\0') && ((*s == *p) || ('.' == *p))) {
                if (isMatch(s, p + 2)) {
                    return true;
                }
                
                ++s;
            }
            
            return isMatch(s, p + 2);
        }
        else {
            if ((*s != '\0') && ((*s == *p) || ('.' == *p))) {
                return isMatch(s + 1, p + 1);
            }
            
            return false;
        }
    }
};