DequeueImpl.java

/**
 * Author: Deepak Singhvi
 */
class DequeueImpl {

  private Deque head;
  private Deque tail;

  public DequeueImpl() {
  }

  public void insertAtFirst(Integer element) {
    Deque newNode = new Deque();
    newNode.setData(element);
    if (isEmpty()) {
      head = tail = newNode;
    } else {
      newNode.next = head;
      head.prev = newNode;
      head = newNode;
    }
  }

  public void insertAtLast(Integer element) {
    Deque newNode = new Deque();
    newNode.setData(element);
    if (isEmpty()) {
      head = tail = newNode;
    } else {
      newNode.prev = tail;
      tail.next = newNode;
      tail = newNode;
    }
  }

  public Integer removeFirst() {
    if (isEmpty()) {
      System.out.println("No element found");
      return null;
    }
    Integer value = head.getData();
    head = head.next;
    head.prev = null;
    return value;
  }

  public Integer removeLast() {
    if (isEmpty()) {
      System.out.println("No element found");
      return null;
    }
    Integer value = tail.getData();
    tail = tail.prev;
    tail.next = null;
    return value;
  }

  public boolean isEmpty() {
    return null == head ? true : false;
  }

  @Override
  public String toString() {
    if (isEmpty()) {
      return "";
    }
    StringBuilder sb = new StringBuilder();
    Deque temp = head;
    while (temp != null) {
      sb.append(temp.getData()).append("->");
      temp = temp.next;
    }
    return sb.toString();
  }
}