1.3.29

Author: gdhucoder

Ch_1_3/Ex_1_3_29.md

@@ -14,11 +14,82 @@ categories:
 
 ## Problem:
 
-Write a Queue implementation that uses a circular linked list, which is the same as a linked list except that no links are null and the value of last.next is first when- ever the list is not empty. Keep only one Node instance variable (last).
+Write a Queue implementation that uses a circular linked list, which is the same as a linked list except that no links are null and the value of last.next is first whenever the list is not empty. Keep only one Node instance variable (last).
 
 ## Solution：
 
 
+**use only one instance variable**
+
+```java
+public static class _Queue<Item> {
+
+    Node tail;
+
+    private class Node {
+
+      public Node(Item item) {
+        this.item = item;
+      }
+
+      Item item;
+      Node next;
+    }
+
+    /**
+     * insert at last
+     */
+    public void enqueue(Item item) {
+      if (tail == null) {
+        tail = new Node(item);
+        tail.next = tail;
+      } else {
+        Node front = tail.next;
+        Node n = new Node(item);
+        tail.next = n;
+        tail = n;
+        tail.next = front;
+      }
+    }
+
+    public void print() {
+      Node cur = tail.next;
+      while (cur != tail) {
+        StdOut.printf("%s->", cur.item);
+        cur = cur.next;
+      }
+      StdOut.println(cur.item);
+    }
+
+    public boolean isEmpty() {
+      return tail == null;
+    }
+
+
+    /**
+     * remove first element in queue
+     */
+    public Item dequeue() {
+      if (tail == tail.next) {
+        Item item = tail.item;
+        tail = null;
+        return item;
+      }
+      Node front = tail.next;
+      Item item = front.item;
+      tail.next = front.next;
+      return item;
+    }
+  }
+```
+
+
+
+
 ## Reference：
 
+[circular-queue-array](https://www.geeksforgeeks.org/circular-queue-set-1-introduction-array-implementation/)
+
+[circular-queue-list](https://www.geeksforgeeks.org/circular-queue-set-2-circular-linked-list-implementation/)
 
+[xiaoheigit](https://github.com/YangXiaoHei/Algorithms/blob/master/Ch_1_3_Bags_Queues_And_Stacks/Practise_1_3_29.java)