JA-Stacks-01.BrowserHistory

import java.util.ArrayDeque;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;


class Main {
  public static void main(String[] args) {

  Scanner sc = new Scanner(System.in);

  ArrayDeque<String> browser = new ArrayDeque<>();
  String input = sc.nextLine();

   while(!input.equals("Home")) {
      if(input.equals("back")) {
        String current = browser.peek();
        if (current == null) {
          System.out.println("no previous URLs");

        } else {
          current = browser.pop();
          if(browser.isEmpty()) {
            System.out.println("no previous URLs");
            browser.push(current);
          }  else {
            System.out.println(browser.peek());
          }
        }

      } else {
        browser.push(input);;
        System.out.println(input);

      }
      input = sc.nextLine();
   }

  }
}