CareerCup

import java.util.Scanner;
import java.util.regex.Pattern;

public class Solution {

	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		
		System.out.println("Enter pattern: "); 
		String pattern = sc.next();
		
		System.out.println("Enter string: ");
		String input = sc.next();
		
		if(Pattern.matches(pattern, input)){
			System.out.println("There is a match");
		} else {
			System.out.println("There isn't a match");
		}
	}

}

import java.util.Scanner;
import java.util.regex.Pattern;

public class Solution {

	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		
		System.out.println("Enter pattern: "); 
		String pattern = sc.next();
		
		System.out.println("Enter string: ");
		String input = sc.next();
		
		if(Pattern.matches(pattern, input)){
			System.out.println("There is a match");
		} else {
			System.out.println("There isn't a match");
		}
	}

}

^[a-zA-Z]*$

/* Adopted from Rob Pike's implementation  */
#include <iostream>
#include <stdio.h>

using namespace std;

bool RegExMatchHelper(char* regex, char* text);

bool RegExMatchKleeneStar (char c, char* regex, char* text){
    do {
        if(RegExMatchHelper(regex, text)) return true;
    } while (*text != '\0' && (*text++ == c || c == '.'));
    
    return false;
}

bool RegExMatchHelper(char* regex, char* text){
    if(regex[0] == '\0') return true;
    if(regex[0] == '$' && regex[1] == '\0') return *text == '\0';
    if(regex[1] == '*') {
        return RegExMatchKleeneStar(regex[0], regex+2, text);
    } 
    if(*text != '\0' && (*text++ == regex[0] || regex[0] == '.')) {
            return RegExMatchHelper(regex+1, text);
    }
    
    return false;
}

bool RegExMatcher (char* regex, char* text){
    if(regex[0] == '\0') return true;
    
    if(regex[0] == '^') {
        return RegExMatchHelper(regex+1, text);
    } else {
        do {
            if(RegExMatchHelper(regex, text)) return true;
        } while (*text++ != '\0');
    }
    
    return false;
}

int main(int argc, char** argv) {
    if(argc != 3) cout << "Wrong format\n";
    if(RegExMatcher(argv[1],argv[2])) cout << "Match\n";
    else cout << "Doesn't match\n";
    return 0;
}