Regular Expression Matching

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class Solution {public:    bool isMatch(string s, string p) {        return match(s,p,0,0);    }private:    bool match(string s,string p,int a,int b) {        int m=s.size();        int n=p.size();        if(a==m&&b==n)return true;        if(b==n)return false;        if(b==n-1||p[b+1]!='*'){            if(a<m&&(s[a]==p[b]||p[b]=='.'))return match(s,p,a+1,b+1);            return false;        }else{            if(match(s,p,a,b+2))return true;            while(a<m&&(s[a]==p[b]||p[b]=='.')){                if(match(s,p,a+1,b+2))return true;                ++a;            }            return false;        }    }};