Expression Pattern matching

/***
Implement regular expression matching with support for ‘.’ and ‘*’.
"." can be any single character
"x*" can represent any # of preceding character, eg "xxx","xx"...

1. API: s and p are char linked list?
2. both s and p can contain matching character".""*", or just p

if *s = *p (check next p is '*')
http://leetcode.com/2011/09/regular-expression-matching.html
***/


#include <iostream>
#include <string>

using namespace std;

bool isMatch(const char *s, const char *p) {
       //base case
       if(*s == '\0' && *p == '\0')
              return true;

       // p next is not '*'
       if(*(p+1) != '*') {
              if(*s != *p && *p != '.' || *s == '\0')
                     return false;
              else return isMatch(s+1, p+1);
       }

       // p next is '*'
       while((*p == *s) || (*p == '.' && *s != '\0')) {
              if(isMatch(s, p+2))
                     return true;
              s++;
       }

       return isMatch(s, p+2);
}

void main() {
       string s = "aab";
       string p = ".b*.*b";

       if (isMatch(&s[0], &p[0]))
       {
              cout<<"match expression"<<endl;
       } else cout<< "not match"<<endl;

}



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