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



class Solution {
public:

//* 匹配0或多个 前面的字符
// "a", "ab*"
    bool isMatch(string s, string p) {
     
        int pLen=p.length();
        int sLen=s.length();
        
        if(pLen==0)
            return sLen==0;
            
        if(pLen==1)
            if( (s[0]==p[0] || p[0]=='.') && sLen==1)
                return true;
            else
                return false;
                
        if(p[1]!='*'){
            if(s.length()>0 && (s[0]==p[0] || p[0]=='.'))
                return isMatch(s.substr(1),p.substr(1));
            else
                return false;
        }else{
            while(s.length()>0 && (p[0]==s[0] || p[0]=='.'))
            {
                if(isMatch(s,p.substr(2)))//*表示0个字符
                    return true;
                s=s.substr(1);
            }
            return isMatch(s,p.substr(2));
        }
    }
};