Didn't notice that problem is not for Java, so I solved it. Maybe someone will need the solution. Solution without checking of stacks for emptiness.


import java.util.ArrayList;
import java.util.HashMap;
import java.util.Scanner;
import java.util.StringTokenizer;

public class HelloWorld {

    public static void main (String[] args)     {
        HashMap<Integer,  ArrayList<Integer>> map = new HashMap<Integer, ArrayList<Integer>>();
        Scanner reader = new Scanner(System.in);
        int n = reader.nextInt();
        reader.nextLine();
        for (int i = 0; i < n; i++) {
            String command = reader.nextLine();
            StringTokenizer tokenizer = new StringTokenizer(command);
            command = tokenizer.nextToken();
            if ("PUSH".equals(command)) {
                int key = Integer.parseInt(tokenizer.nextToken());
                int value = Integer.parseInt(tokenizer.nextToken());
                if (map.containsKey(key)) {
                    map.get(key).add(0, value);
                }
                else {
                    map.put(key, new ArrayList<Integer>());
                    map.get(key).add(0, value);
                }
            }
            else if ("POP".equals(command)) {
                int key = Integer.parseInt(tokenizer.nextToken());
                if (map.containsKey(key)) {
                    System.out.println(map.get(key).get(0));
                    map.get(key).remove(0);
                }
            }

        }
    }
}

Edited by author 31.10.2016 23:24

Edited by author 31.10.2016 23:26