08. Simple Text Editor

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

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int lines = Integer.parseInt(scan.nextLine());
        StringBuilder text = new StringBuilder();
        Deque<StringBuilder> stack = new ArrayDeque();
         while (lines-- > 0){
             String[] line = scan.nextLine().split(" ");
             String comand = line[0];
             switch (comand){
                 case "1":
                     text.append(line[1]);
                     stack.push(new StringBuilder(text));
                     break;
                 case "2":
                     int count = Integer.parseInt(line[1]);
                     int start = text.length() - count;
                     text.delete(start, start + count);
                     stack.push(new StringBuilder(text));
                     break;
                 case "3":
                     System.out.println(text.charAt(Integer.parseInt(line[1])-1));
                     break;
                 case "4":
                     if (stack.size() > 1){
                         stack.pop();
                         text = stack.peek();
                     }else if (stack.size() == 1){
                             text = new StringBuilder();
                         }
                     break;
             }
         }
    }
}