题解 | 好串

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Scanner;

// 参考：https://blog.nowcoder.net/n/f031ce972f8f4f358b2b086981dfe5cb
// 好串，模式匹配
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String s = in.nextLine();

        Deque<Character> st = new ArrayDeque<>(); 

        for(char c : s.toCharArray()){
            if(c == 'a'){
                st.push(c);
            }else if(c == 'b'){
                if(st.isEmpty()){
                    System.out.println("Bad");
                    in.close();
                    return;
                }
                st.pop();
            }else{
                System.out.println("Bad");
                in.close();
                return;
            }
        }
        if(st.isEmpty()){
            System.out.println("Good");
        }else{
            System.out.println("Bad");
        }
    }
}