Regular Expression Matching（leetcode）

'.'

'*'

'.' 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

class Solution {
public:
bool isMatch(string s, string p) {
if (s == "" && p == "") return true;
if ((p.length() > 1 && p[1] != '*') || p.length() == 1) {
if (s == "") return false;
if (p[0] != s[0] && p[0] != '.') {
return false;
} else {
return isMatch(s.substr(1, s.length()-1), p.substr(1, p.length()-1));
}
} else {
if (p == "") return false;
if (isMatch(s, p.substr(2, p.length()-2))) return true;
if (s == "") return false;
for (int i = 0; i < s.length(); ++i) {
if (s[i] == p[0] || (s[i] != p[0] && p[0] == '.')) {
if (isMatch(s.substr(i+1, s.length()-i-1), p.substr(2, p.length()-2))) return true;
} else {
if (i == 0) return isMatch(s, p.substr(2, p.length()-2));
else break;
}
}
return false;
}
}
};