Regular Expression için Algoritma

#include <iostream>
#include <string>
using namespace std;
bool isMatch(string s, string p);
int main(void)
{
    bool check;
    string re, in;
    //cout<<"Enter Regular Expression and Input: ";
    cin>>re>>in;
    check=isMatch(in,re);
    if(check==true)
        cout<<"ACCEPT";
    else if(check==false)
        cout<<"REJECT";

    return 0;
}
bool isMatch(string input, string regex)
{
    if (regex.empty()) return input.empty();
    if (regex[1] != '*')
    {
        if(input[0] == regex[0] || (regex[0] == '.' && input[0] != '\\0'))
            return isMatch(input.substr(1), regex.substr(1));
        else
            return false;
    }
    else
    {
        if (isMatch(input, regex.substr(2)))
            return true;
        int index = 0;
        while (index < input.size() && (input[index] == regex[0] || regex[0] == '.'))
        {
            if (isMatch(input.substr(++index), regex.substr(2)))
                return true;
        }
        return false;
    }
}