【数据结构】双链表

版权声明：无意呢。 https://blog.csdn.net/qq_41900081/article/details/86546989

双链表的优点：

对于链表中的一个结点，拥有两个指针，一个指向前驱结点，一个指向后继结点，因此可以从两个方向继续操作

双链表的缺点：

1） 每个结点需要议案家一个额外的指针，因此需要更多的空间开销
2）结点的插入或删除操作更加费时（需要更多的指针操作）、

双链表的基本操作

1. 插入操作
   1）前插
   2）尾插
   3）中间插入
2. 删除操作
   1）删除头结点
   2）删除尾结点
   3）删除中间结点

Java代码实现

package dataStructure;

class DDLNode{
	int data;
	DDLNode previous = null;
	DDLNode next = null;
	
	public DDLNode(int d) {
		data = d;
	}
	
}

public class DDList{
	//头结点
	DDLNode head;
	
	public DDList() {
		head = null;
	}
	
	//获取双链表长度
	int size() {;
		if(head == null)  return 0;
		int len = 1;
		DDLNode cur = head;
		while(cur.next != null) {
			len++;
			cur = cur.next;
		}
		return len;
	}
	
	//打印双链表
	void Print() {
		DDLNode cur = head;
		if(cur == null) System.out.println("null");
		
		while(cur != null) {
			System.out.print(cur.data+"->");
			cur = cur.next;
		}
		System.out.println();
	}
	
	//插入结点
	DDLNode Insert(DDLNode node,int position) {
		DDLNode pre = head;
		//双链表为空
		if(head == null) {
			if(position != 1) {
				System.out.println("非法插入");
				return head;
			}
			head =  node;
			return head;
		}
		//非法插入
		if(position < 1 || position > size()+2) {
			System.out.println("非法插入");
			return head;
		}
		if(position == 1) {
			node.next = pre;
			pre.previous = node;
			head = node;
			return head; 
		}else {
			int count = 1;
			//找到插入的位置
			while(count < position - 1) {
				pre = pre.next;
				count++;
			}
			
			DDLNode cur = pre.next;			
			node.next = cur;
			pre.next = node;
			node.previous = pre;
			if(cur != null)
				cur.previous = node;
		}
		return head;
	}
	
	//删除指定结点
	DDLNode deleteDDLNode(int position) {
		if(head == null)  {
			System.out.println("双链表为空，不允许删除");
			return head;
		}
		if(position > size() || position < 1) {
			System.out.println("非法删除");
			return head;
		}
		if(position == 1) {
			DDLNode del = head;
			head = head.next;
			head.previous = null;
			return del;
		}else {
			DDLNode pre = head;
			int count = 1;
			while(count < position - 1) {
				pre = pre.next;
				count++;
			}
			DDLNode del = pre.next;
			pre.next = del.next;
			if(del.next != null)
				del.next.previous = pre;
			del.next = null;
			del.previous = null;
			
			return del;
		}
		
	}
	public static void main(String[] args) {
		DDList list = new DDList();
		
		list.Insert(new DDLNode(1), 1);
		list.Insert(new DDLNode(2), 2);
		list.Insert(new DDLNode(5), 2);
		list.Print();
		list.deleteDDLNode(3);
		list.Print();
		
	}
}