LeetCode [10. Regular Expression Matching]

Problem

10. Regular Expression Matching

Question

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") → falseisMatch("aa","aa") → trueisMatch("aaa","aa") → falseisMatch("aa", "a*") → trueisMatch("aa", ".*") → trueisMatch("ab", ".*") → trueisMatch("aab", "c*a*b") → true

Code

class Solution {public:    bool isMatch(string s, string p) {        if (p.size() == 0) return s.size() == 0;        bool firstmatch = (!s.empty()) && ((s[0] == p[0]) || p[0] == '.');        if (p.size() > 1 && p[1] == '*') {            return (isMatch(s, p.substr(2)) || firstmatch && isMatch(s.substr(1), p));        }        else            return firstmatch && isMatch(s.substr(1), p.substr(1));    }};