content: /*
   * Copyright (C) 2011 Clearspring Technologies, Inc. 
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.clearspring.analytics.util;
  
  import java.util.ConcurrentModificationException;
  import java.util.Iterator;
  
  public class DoublyLinkedList<T> implements Iterable<T> {
  
      protected int size;
      protected ListNode2<T> tail;
      protected ListNode2<T> head;
  
      /**
       * Append to head of list
       */
      public ListNode2<T> add(T value) {
          ListNode2<T> node = new ListNode2<T>(value);
          if (size++ == 0) {
              tail = node;
          } else {
              node.prev = head;
              head.next = node;
          }
  
          head = node;
  
          return node;
      }
  
      /**
       * Prepend to tail of list
       */
      public ListNode2<T> enqueue(T value) {
          ListNode2<T> node = new ListNode2<T>(value);
          if (size++ == 0) {
              head = node;
          } else {
              node.next = tail;
              tail.prev = node;
          }
  
          tail = node;
  
          return node;
      }
  
      public void add(ListNode2<T> node) {
          node.prev = head;
          node.next = null;
  
          if (size++ == 0) {
              tail = node;
          } else {
              head.next = node;
          }
  
          head = node;
      }
  
      public ListNode2<T> addAfter(ListNode2<T> node, T value) {
          ListNode2<T> newNode = new ListNode2<T>(value);
          addAfter(node, newNode);
          return newNode;
      }
  
      public void addAfter(ListNode2<T> node, ListNode2<T> newNode) {
          newNode.next = node.next;
          newNode.prev = node;
          node.next = newNode;
          if (newNode.next == null) {
              head = newNode;
          } else {
              newNode.next.prev = newNode;
          }
          size++;
      }
  
      public void remove(ListNode2<T> node) {
          if (node == tail) {
              tail = node.next;
          } else {
              node.prev.next = node.next;
          }
  
          if (node == head) {
              head = node.prev;
          } else {
              node.next.prev = node.prev;
          }
          size--;
      }
  
      public int size() {
          return size;
      }
  
  
      @Override
      public Iterator<T> iterator() {
          return new DoublyLinkedListIterator(this);
      }
  
      protected class DoublyLinkedListIterator implements Iterator<T> {
  
          protected DoublyLinkedList<T> list;
          protected ListNode2<T> itr;
          protected int length;
  
          public DoublyLinkedListIterator(DoublyLinkedList<T> list) {
              this.length = list.size;
              this.list = list;
              this.itr = list.tail;
          }
  
          @Override
          public boolean hasNext() {
              return itr != null;
          }
  
          @Override
          public T next() {
              if (length != list.size) {
                  throw new ConcurrentModificationException();
              }
              T next = itr.value;
              itr = itr.next;
              return next;
          }
  
          @Override
          public void remove() {
              throw new UnsupportedOperationException();
          }
  
      }
  
      public T first() {
          return tail == null ? null : tail.getValue();
      }
  
      public T last() {
          return head == null ? null : head.getValue();
      }
  
      public ListNode2<T> head() {
          return head;
      }
  
      public ListNode2<T> tail() {
          return tail;
      }
  
      public boolean isEmpty() {
          return size == 0;
      }
  
      @SuppressWarnings("unchecked")
      public T[] toArray() {
          T[] a = (T[]) new Object[size];
          int i = 0;
          for (T v : this) {
              a[i++] = v;
          }
          return a;
      }
  }
  