双向链表也叫双链表，是链表的一种，它的每个数据结点中都有两个指针，分别指向直接后继和直接前驱。所以，从双向链表中的任意一个结点开始，都可以很方便地访问它的前驱结点和后继结点。
2.双向链表的插入与删除操作 插入 删除 代码实现 public class DoubleLinked { private class Node{ public int getData() { return data; } public void setData(int data) { this.data = data; } public Node getNext() { return next; } public void setNext(Node next) { this.next = next; } private int data; private Node next; private Node prior; public Node getPrior() { return prior; } public void setPrior(Node prior) { this.prior = prior; } public Node(int data, Node next,Node prior){ this.data = data; this.next = next; this.prior = prior; } } private Node head; //头插法 public void headinsert (int data){ Node node = new Node(data,null,null); if (null == this.head){ this.head = node; return; } node.setNext(this.head); this.head.setPrior(node); this.head = node; } //尾插法 public void tailinsert(int data){ Node node = new Node(data,null,null); if (null == this.head){ this.head = node; return; } Node p = this.head; while (null != p.getNext()){ p = p.getNext(); } node.setPrior(p); p.setNext(node); } //中间插入法 public void midinsert(int data){ Node node = new Node(data,null,null); if (null == this.head){ this.head = node; return; } if (this.head.getData() > data){ node.setNext(this.head); this.head.setPrior(node); this.head = node; return; } Node p = this.head; while (null != p.getNext()){ if (p.getNext().getData() > data ){ break; } p = p.getNext(); } if (null == p.getNext()) { node.setPrior(p); p.setNext(node); return; } node.setPrior(p); node.setNext(p.getNext()); p.getNext().setPrior(node); p.setNext(node); } //删除操作 public void remove(int data) { if (null == this.head) { System.out.println("链表为空！"); return; } if (this.head.getData() == data) { this.head = this.head.getNext(); print(); return; } Node p = this.head; while (null != p.getNext()) { if (p.getNext().getData() == data) { break; } p = p.getNext(); } if (null == p.getNext()) { System.out.println(data + " 不存在！"); } else { p.setNext(p.getNext().getNext()); if (null != p.getNext()) { p.getNext().setPrior(p); } print(); }// p.getPrior().setNext(p.getNext());// p.getNext().setPrior(p.getPrior()); } //打印链表 public void print(){ if (null == this.head){ return; } Node p = this.head; while(null != p){ System.out.print(p.getData()+" "); p = p.getNext(); } System.out.println(); } public static void main(String[] args) { DoubleLinked list = new DoubleLinked(); list.headinsert(5); list.headinsert(3); list.headinsert(7); list.headinsert(2);// list.midinsert(11);// list.midinsert(5);// list.midinsert(3);// list.midinsert(9); list.tailinsert(4); list.tailinsert(1); list.tailinsert(6); list.tailinsert(8); list.print(); System.out.println("删除后------"); list.remove(8); }}输出结果：
2 7 3 5 4 1 6 8 删除后------2 7 3 5 4 1 6 3.循环链表的定义将单链表中终端结点的指针端自空指针改为指向头结点，就使整个单链表形成一个环，这种头尾:相接的单链表称为单循环链表，简称循环链表( circular linkedlist) 。
单向循环链表是单链表的另一种形式，其结构特点是链表中最后一个结点的指针不再是结束标记，而是指向整个链表的第一个结点，从而使单链表形成一个环。
循环单链表的优点是从链尾到链头比较方便。当要处理的数据元素序列具有环型结构特点时，适合于采用循环单链表。
4.循环链表的插入与删除代码实现 public class CircleLinked { private class Node{ public int getData() { return data; } public void setData(int data) { this.data = data; } public Node getNext() { return next; } public void setNext(Node next) { this.next = next; } private int data; private Node next; private Node prior; public Node getPrior() { return prior; } public void setPrior(Node prior) { this.prior = prior; } public Node(int data, Node next,Node prior){ this.data = data; this.next = next; this.prior = prior; } } Node head ; Node tail ; //头插法（可变参数） public void headInsert(int... data){ if (null == data || 0 == data.length) { return; } for (int d : data) { Node node = new Node(d,null,null); if (head == null){ head = node; tail = node; continue; } node.setNext(head); head = node; tail.setNext(head); } } //尾插法（可变参数） public void tailInsert(int... data) { if (null == data || 0 == data.length) { return; } for (int d : data) { Node node = new Node(d, null, null); if (head == null) { head = node; this.head.setNext(this.head); tail = node; continue; } Node p = this.head; while (head != p.getNext()) { p = p.getNext(); } node.setPrior(p); p.setNext(node); tail.setNext(head); } } //判断是否为循环链表 public boolean isCircle(){ Node fast = head; Node slow = head; if (head == null || head.getNext() == null){ return false; } while(null != head){ fast = fast.getNext().getNext(); slow = slow.getNext(); if (fast == slow){ break; }else if (fast == null || fast.getNext() == null){ return false; } } return true; } //删除节点 public void remove(int data){ if (null == this.head ){ System.out.println("链表为空！"); return; } if (this.head.getData() == data){ this.head = this.head.getNext(); this.tail.setNext(head); return; } Node p = this.head; while(head != p.getNext()){ if (p.getNext().getData() == data){ break; } p = p.getNext(); } if (head != p.getNext()){ p.setNext(p.getNext().getNext()); }else{ System.out.println(data + " 不存在！"); } } //打印链表 public void print(){ if (head == null){ return; } Node p = head; while (p.getNext() != head) { System.out.println(p.getData()+" "); p = p.getNext(); } System.out.println(p.getData()); } public static void main(String[] args) { CircleLinked linked = new CircleLinked(); linked.headInsert(3,6,8,4,9,1); linked.print(); System.out.println(linked.isCircle()); linked.remove(3); linked.print(); }}
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