数据结构 -- 双向链表 linkedList 手写

双向链表 linkedList

package list;



public class LinkedList<E> {
	
	
	transient int size = 0;

    transient Node<E> first;

    transient Node<E> last;

    
    public LinkedList() {
    }
	
    public void  add(E e){
    	linkedLast(e);
    	size++;
    }
		
	private void linkedLast(E e) {
		// TODO Auto-generated method stub
		Node<E> newNode = new Node<E>(last, e, null);
		
		System.out.println("e=="+e);
		
		//先保存起来last
		Node<E> l = last;
		
		//将最后一个last指向新元素
		last = newNode;
		
		//当last为空时 first指向元素 否则 将最后一个元素的next 指向新节点
		if (l ==null) {
			first = newNode;
		}else{
			l.next = newNode;	
		}
		
	}
	
	/**
	 * 在任意位置添加元素
	 * @param index
	 * @param e
	 */
	public void  add(int index,E e){
		if (index<0 || index >size || e == null) {
			return;
		}

		//当是在尾部添加元素时
		if (index == size) {
			linkedLast(e);
		}else{
			Node<E> p = node(index);
			//当时在头部添加元素时
			if (index == 0) {
				Node<E> newNode = new Node<E>(null, e, p);
				p.prev = newNode;
				first = newNode;
				
			}else{
				//找到index节点的p的prev节点			
				Node<E> pp = p.prev;
				//创建要添加的e的节点对象	并将它的前节点和后节点设置	
				Node<E> newNode = new Node<E>(pp, e, p);
				//将前一个节点的下一个节点指向新节点
				pp.next = newNode;
				//将原来p节点的上一个节点设置给新节点
				p.prev = newNode;
			}
			
		}
		size++;
	}
	
	public void remove(int index) {
		Node<E> target = node(index);
		unlinked(target);
		size --;
	}

	private void unlinked(Node<E> p){
		//当是顶点节点时
		if (p.prev == null) {
			first = p.next;
		}else{
			p.prev.next = p.next;
		}
		
		//当时尾部节点时
		if (p.next == null) {
			last = p.prev;
		}else{
			p.next.prev = p.prev;
		}
		
	}
	
	private static class Node<E> {
        E item;
        Node<E> next;
        Node<E> prev;

        Node(Node<E> prev, E element, Node<E> next) {
            this.item = element;
            this.next = next;
            this.prev = prev;
        }
    }

	public E get(int index) {
		
		if (index<0 || index >size) {
			return null;
		}
		
		return node(index).item;
		
		
	}

	private Node<E> node(int index) {
		// TODO Auto-generated method stub
		//优化算法
		if (index < (size>>1)) {
			Node<E> node = first;
			for (int i = 0; i < index; i++) {
				node = node.next;
			}
			return node;
		}else{
			Node<E> node1 = last;
			for (int i = size -1; i > index; i--) {
				node1 = node1.prev;
			}
			return node1;
		}
	}

	
	
}
测试代码

package list;

public class TestMain {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		LinkedList<String> linkedList = new LinkedList<>();
		linkedList.add("aaaa");
		linkedList.add("bbbb");
		linkedList.add("cccc");
		
		linkedList.add(0,"dddd");
		
		linkedList.add(1,"eeee");
		
		for (int i = 0; i < linkedList.size; i++) {
			System.out.print(linkedList.get(i)+"--"+linkedList.get(i+1)+"  ");
		}
		
		System.out.println();
		linkedList.remove(0);
		
		for (int i = 0; i < linkedList.size; i++) {
			System.out.print(linkedList.get(i)+"--"+linkedList.get(i+1)+"  ");
		}
		
	}

}