循环链表

Author: FantasyLWX

README.md

@@ -35,8 +35,10 @@
 ## 链表
 
 * [实现一个单链表，支持增删操作][single-linked-list]
+* [实现一个循环链表，支持增删操作][circular-linked-list]
 
 [single-linked-list]: ./src/com/fantasy/datastructure/linkedlist/SingleLinkedList.java
+[circular-linked-list]: ./src/com/fantasy/datastructure/linkedlist/CircularLinkedList.java
 
 ## 算法
 

src/com/fantasy/datastructure/linkedlist/CircularLinkedList.java

@@ -0,0 +1,99 @@
+package com.fantasy.datastructure.linkedlist;
+
+/**
+ * 循环链表
+ *
+ * <pre>
+ *     author  : Fantasy
+ *     version : 1.0, 2020-07-03
+ *     since   : 1.0, 2020-07-03
+ * </pre>
+ */
+public class CircularLinkedList {
+    private ListNode head;
+    private ListNode tail;
+
+    public CircularLinkedList() {
+        head = null;
+        tail = null;
+    }
+
+    public void insertHead(int value) {
+        insertHead(new ListNode(value));
+    }
+
+    public void insertHead(ListNode node) {
+        if (head == null) {
+            node.next = node;
+            head = tail = node;
+        } else {
+            node.next = head;
+            tail.next = node;
+            head = node;
+        }
+    }
+
+    public void insertTail(int value) {
+        insertTail(new ListNode(value));
+    }
+
+    public void insertTail(ListNode node) {
+        if (head == null) {
+            node.next = node;
+            head = tail = node;
+        } else {
+            node.next = head;
+            tail.next = node;
+            tail = node;
+        }
+    }
+
+    public void deleteHead() {
+        if (head == null) {
+            return;
+        }
+
+        if (head == tail) {
+            head = tail = null;
+            return;
+        }
+
+        head = head.next;
+        tail.next = head;
+    }
+
+    public void deleteTail() {
+        if (tail == null) {
+            return;
+        }
+
+        if (head == tail) {
+            head = tail = null;
+            return;
+        }
+
+        ListNode temp = head;
+        while (temp.next != tail) {
+            temp = temp.next;
+        }
+
+        temp.next = head;
+        tail = temp;
+    }
+
+    public String toString() {
+        StringBuilder sb = new StringBuilder();
+        sb.append("[");
+        for (ListNode node = head; node != null; node = node.next) {
+            sb.append(node.val);
+            if (node.next != head) {
+                sb.append(",").append(" ");
+            } else {
+                break;
+            }
+        }
+        sb.append("]");
+        return sb.toString();
+    }
+
+}

src/com/fantasy/datastructure/linkedlist/test/CircularLinkedListTest.java

@@ -0,0 +1,33 @@
+package com.fantasy.datastructure.linkedlist.test;
+
+import com.fantasy.datastructure.linkedlist.CircularLinkedList;
+
+/**
+ * “循环链表”的测试类
+ *
+ * <pre>
+ *     author  : Fantasy
+ *     version : 1.0, 2020-07-03
+ *     since   : 1.0, 2020-07-03
+ * </pre>
+ */
+public class CircularLinkedListTest {
+
+    public static void main(String[] args) {
+        CircularLinkedList list = new CircularLinkedList();
+
+        list.insertHead(1);
+        System.out.println(list); // [1]
+
+        list.insertHead(2);
+        list.insertTail(3);
+        System.out.println(list); // [2, 1, 3]
+
+        list.deleteHead();
+        System.out.println(list); // [1, 3]
+
+        list.deleteTail();
+        System.out.println(list); // [1]
+    }
+
+}