Java 数据结构之双端链表

版权声明：聂CC~ https://blog.csdn.net/ncc1995/article/details/86719330

写双端链表简直是写双向链表的基础，重点是插入和删除操作时对first以及last结点的修改。其他的就没啥了吧。

package linkList;

/*
 * 结点定义
 */
class Node{
	Object data;
	Node next;
	
	public Node(Object d) {
		this.data = d;
		this.next = null;
	}
	
	public void display() {
		System.out.print(data + " ");
	}
}

/*
 * 写一个双端链表
 */
public class firstlastList {
	Node first;
	Node last;
	
	/*
	 * 构造器
	 */
	public firstlastList() {
		this.first = null;
		this.last = null;
	}
	
	/*
	 * 从头插入
	 */
	public void insertFirst(Object data) {
		Node newNode = new Node(data);
		
		if (isEmpty()) {
			last = newNode;
		}
		
		newNode.next = first;
		first = newNode;
	}
	
	
	/*
	 * 从尾部插入
	 */
	//无论怎样都要把newNode赋值给first和last
	public void insertLast(Object data) {
		Node newNode = new Node(data);
		
		if (isEmpty()) {
			first = newNode;
		}else {
			last.next = newNode;
		}
		last = newNode;
	}
	
	/*
	 * 任意位置插入结点
	 */
	public void insertLoc(int loc, Object d) {
		Node current = first;
		int j = 1;
		
		Node newNode = new Node(d);
		
		if(loc<1 || loc > length()+1) {
			System.out.println("The location is not exit!");
			return;
		}
		
		if(loc == j) {
			newNode.next = current;
			first = newNode;
			return;
		}
		
		//定位到location-1的位置了
		while(j<loc-1 & current!=null) {
			current = current.next;
			j++;
		}
		
		if(current == last) {
			last = newNode;
		}
		newNode.next =current.next;
		current.next = newNode;
		System.out.println("last "+ last.data);
	}
	
	
	/*
	 * 一定要记得对last的处理
	 * (1) 当删除的结点只有一个结点时，记得要对last置空，而first
	 *     执行了first = first.next会自动置空
	 * (2) 当不只有一个结点时，遍历到location-1位置的结点，需要先
	 *     令last = current，再进行删除操作
	 * 对首结点删除也需要注意
	 * (1) 对首结点删除只需要执行first = first.next操作就可以，而
	 *     不必再执行current.next = current.next.next   //将删除的前一个结点指向删除的下一个结点
	 */
	public void delete(int loc) {
		Node current = first;
		int j = 1;
		System.out.println("开始的last："+last.data);

		if(loc<1 || loc>length()) {
			System.out.println("The location to delete is not exit!");
			return;
		}
		
		if(loc == j) {
			if(first == last) {
				last = null;
			}
			first = current.next;
			return;
		}
		
		//遍历到current为第location-1的位置
		while(j<loc-1) {
			current = current.next;
			j++;
		}
		
		if(current.next == last) {
			last = current;
		}
		current.next = current.next.next;
		System.out.println("first:" + first);
		System.out.println("删除后的last："+last);
	}
	
	/*
	 * 判断是否为空
	 */
	public boolean isEmpty() {
		
		return(first == null);
	}
	
	public int length() {
		int length = 0;
		Node current = first;
		
		while(current != null) {
			length++;
			current = current.next;
		}
		
		return length;
	}
	
	public void displayList() {
		Node temp = first;
		while(temp != null) {
			temp.display();
			temp = temp.next;
		}
		System.out.println();
	}
	
	//main
	public static void main(String[] args) {
		firstlastList list = new firstlastList();
		
		list.insertFirst(22);
		list.displayList();
		list.insertLoc(3, 3);
		list.displayList();

	}
}