Stack

/*
   GENERAL TASK DESCRIPTION

   Implement barebones (meaning - no getters/setters, or anything extraneous
   In task descriptions after data structure name the required interface (list of public methods) is in parentheses
   Use proper formatting. Implement each data structure in a separate class. For Node classes use inner classes.
   For brevity use primitive integer as value type (no generics).
*/

// Task 1 - singly-linked list (add, get, remove) add(), get(i), remove(i), remove(O)

// Task 2 - stack (push, pop)

// Task 3 - queue (offer, poll)

// Task 4 - flexible-size list (using arrays - think of ArrayList) - (add, get, remove, insert)


class Stack {
  private Node last;

  public void push(Integer value) {

  	if (last == null)
      last = new Node(value, null);
    else {
      Node node = new Node(value, last);
      last = node;
    }
  }

  public Integer pop() { // get should return the value, not the node

    if (last == null)
      throw new IllegalStateException();

    Node node = last;
    last = last.next;

    return node.value;
  }

  public Integer top() {

    if (last == null)
      throw new IllegalStateException();

    return last.value;
  }

  public boolean empty() {
    return last == null;
  }

  static class Node {
    public Integer value;
    public Node next;

    Node(Integer value, Node next) {
      this.value = value;
      this.next = next;
    }
  }

}