Regular Expression Matching--LeetCode

Regular Expression Matching

'.'

'*'

'.' 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

Solution：

class Solution {
public:
bool isMatch(string s, string p) {
if (p.length() == 0) return s.length() == 0;
if (p[1] == '*')
{
//isMatch("aab", "c*a*b") → true,返回isMatch("aab", "a*b")
//isMatch("aa", "a*") → true，返回isMatch("a", "a*")
//isMatch("aa", ".*") → true，返回isMatch("a", ".*")
//isMatch("a", ".*") → true，返回isMatch("", "")
return isMatch(s, p.substr(2)) || (s.length() != 0 && (s[0] == p[0] || p[0] == '.') && isMatch(s.substr(1), p));
}
else
{
if (s.length() != 0 && (s[0] == p[0] || p[0] == '.')) return isMatch(s.substr(1), p.substr(1));
return false;
}
}
};