THIN-uebung2/src/Aufgabe1_Kellerautomat.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class Aufgabe1_Kellerautomat {
    private static String[] words = {"ZZO", "ZZOZZOO", "ZZZOO", "ZZOO", "ZZOZZO", "ZOZ"};

    public static void main(String[] args) {
        for (String word : words) {
            calculate(word);
        }
    }

    public static boolean calculate(String word) {
        List<Character> wordChars = new ArrayList<>();
        for (char symbol : word.toCharArray()) {
            wordChars.add(symbol);
        }
        ArrayList<Character> stack = new ArrayList<>();
        stack.add('$');

        int state = 0; //case 0 - 5 = q0 - q5, case -1 = Abfallzustand

        while (wordChars.size() > 0 || state >= 3) {
            char symbol;
            Character stackSymbol = stack.remove(stack.size() - 1);
            switch (state) {
                case 0:
                    if (wordChars.remove(0) == 'Z' && stackSymbol == '$') {
                        stack.add('$');
                        stack.add('Z');
                        state = 1;
                    } else {
                        dontAccept(word);
                        return false;
                    }
                    break;
                case 1:
                    if (wordChars.remove(0) == 'Z' && stackSymbol == 'Z') {
                        stack.add('Z');
                        stack.add('Z');
                        state = 2;
                    } else {
                        dontAccept(word);
                        return false;
                    }
                    break;
                case 2:
                    symbol = wordChars.remove(0);
                    if (isOperator(symbol) && stackSymbol == 'Z') {
                        state = 3;
                    } else if (symbol == 'Z' && stackSymbol == 'Z') {
                        stack.add('Z');
                        stack.add('Z');
                        state = 2;
                    } else if (symbol == 'Z' && stackSymbol == '$') {
                        stack.add('$');
                        stack.add('Z');
                        state = 2;
                    } else {
                        dontAccept(word);
                        return false;
                    }
                    break;
                case 3:
                    if (stackSymbol == 'Z') {
                        stack.add('Z');
                        state = 4;
                    } else {
                        dontAccept(word);
                        return false;
                    }
                    break;
                case 4:
                    if (wordChars.size() > 0) {
                        symbol = wordChars.remove(0);
                        if (symbol == 'Z' && stackSymbol == 'Z') {
                            stack.add('Z');
                            stack.add('Z');
                            state = 2;
                        } else if (isOperator(symbol) && stackSymbol == 'Z') {
                            state = 3;
                        } else {
                            dontAccept(word);
                            return false;
                        }
                    } else {
                        if (stackSymbol == 'Z') {
                            state = 5;
                        } else {
                            dontAccept(word);
                            return false;
                        }
                    }
                    break;
                case 5:
                    if (stackSymbol == '$') {
                        stack.add('$');
                        state = 6;
                    } else {
                        dontAccept(word);
                        return false;
                    }
                    break;
                case 6:
                    accept(word);
                    return true;

            }
        }
        dontAccept(word);
        return false;
    }

    private static void dontAccept(String word) {
        System.out.println("Word: " + word  + "\nnot accepted");
    }

    private static void accept(String word) {
        System.out.println("Word: " + word  + "\naccepted ");
    }

    private static boolean isOperator(char symbol){
        return symbol == '+' || symbol == '*';
    }

}