028_自己实现一个LinkedList

/**
 * 自定义链表
 */
public class MyLinkedList {
	private Node first;
	private Node last;
	
	private int size;
	
	/**
	 * 构造方法
	 */
	public MyLinkedList() {}
	
	/**
	 * 链表大小
	 * @return
	 */
	public int size() {
		return size;
	}
	
	/**
	 * 数组是否为空
	 * @return
	 */
	public boolean isEmpty() {
		return size == 0;
	}
	
	/**
	 * 检测下标是否越界
	 * @param index
	 */
	private void checkElementIndex(int index) {
		if(!(index >= 0 && index < size)) {
			throw new IndexOutOfBoundsException();
		}
	}
	
	/**
	 * 插入元素位置是否合法
	 * @param index
	 * @return
	 */
	private void checkPositionIndex(int index) {
		if(!(index >= 0 && index <= size)) {
			throw new IndexOutOfBoundsException();
		}
	}
	
	/**
	 * 往链表结尾插入元素
	 * @param o
	 */
	private void linkLast(Object o) {
		Node temp = last;
		Node newNode = new Node(temp, o, null);
		last = newNode;
		
		if(temp == null) {
			first = newNode;
		}else {
			temp.next = newNode;
		}
		
		size++;
	}
	
	/**
	 * 往某个节点之前插入元素
	 * @param o
	 * @param x
	 */
	private void linkBefore(Object o, Node x) {
		Node pre = x.prev;
		Node newNode = new Node(pre, o, x);
		x.prev = newNode;
		if(pre == null) {
			first = newNode;
		}else {
			pre.next = newNode;
		}
		
		size++;
	}
	
	/**
	 * 添加元素
	 * @param o
	 * @return
	 */
	public boolean add(Object o) {
		linkLast(o);
		
		return true;
	}
	
	/**
	 * 
	 * @param index
	 * @param o
	 * @return
	 */
	public void add(int index, Object o) {
		checkPositionIndex(index);
		
		if(index == size) {
			linkLast(o);
		}else {
			linkBefore(o, node(index));
		}
	}
	
	/**
	 * 根据下标获取节点
	 * @param index
	 * @return
	 */
	private Node node(int index) {
		if(index < (size >> 1)) {
			Node x = first;
			for(int i = 0; i < index; i++) {
				x = x.next;
			}
			return x;
		}else {
			Node x = last;
			for(int i = size - 1; i > index; i--) {
				x = x.prev;
			}
			return x;
		}
	}
	
	/**
	 * 根据下标获取元素
	 * @param index
	 * @return
	 */
	public Object get(int index) {
		checkElementIndex(index);
		
		return node(index).item;
	}
	
	/**
	 * 删除元素
	 * @param x
	 * @return
	 */
	private Object unlink(Node x) {
		Object element = x.item;
		Node next = x.next;
		Node prev = x.prev;
		
		if(prev == null) {
			first = next;
		}else {
			prev.next = next;
			x.prev = null;
		}
		
		if(next == null) {
			last = prev;
		}else {
			next.prev = prev;
			x.next = null;
		}
		
		x.item = null;
		
		size--;
		
		return element;
	}
	
	/**
	 * 根据下标删除元素
	 * @param index
	 * @return
	 */
	public Object remove(int index) {
		checkElementIndex(index);
		return unlink(node(index));
	}
	
	/**
	 * 根据元素删除
	 * @param o
	 * @return
	 */
	public boolean remove(Object o) {
		if(o == null) {
			for(Node x = first; x != null; x = x.next) {
				if(x.item == null) {
					unlink(x);
					return true;
				}
			}
		}else {
			for(Node x = first; x != null; x = x.next) {
				if(o.equals(x.item)) {
					unlink(x);
					return true;
				}
			}
		}
		
		return false;
	}
	
}

class Node {
	Node prev;
	Object item;
	Node next;
	
	public Node() {}
	
	public Node(Node prev, Object item, Node next){
		this.prev = prev;
		this.item = item;
		this.next = next;
	}
}