add linked queue

realDuYuanChao · realDuYuanChao · commit ca482c6d2291 · 2020-10-24T10:04:41.000+08:00
diff --git a/src/main/java/com/examplehub/datastructures/queue/LinkedQueue.java b/src/main/java/com/examplehub/datastructures/queue/LinkedQueue.java
@@ -0,0 +1,101 @@
+package com.examplehub.datastructures.queue;
+
+import com.examplehub.datastructures.linkedlist.Node;
+
+import java.util.StringJoiner;
+
+public class LinkedQueue<E> {
+
+    /**
+     * The front pointer of LinkedQueue.
+     */
+    private Node<E> front;
+
+    /**
+     * The rear pointer of LinkedQueue.
+     */
+    private Node<E> rear;
+
+    /**
+     * The number of elements in LinkedQueue.
+     */
+    private int size;
+
+    public LinkedQueue() {
+        front = rear = null;
+    }
+
+    /**
+     * Remove item from the front of LinkedQueue.
+     *
+     * @return the item at the front of LinkedQueue.
+     * @throws IllegalAccessError if LinkedQueue is empty.
+     */
+    public E dequeue() throws IllegalAccessException {
+        if (size == 0) {
+            throw new IllegalAccessException();
+        }
+        E retValue = front.data;
+        if ((front = front.next) == null) {
+            rear = null;
+        }
+        size--;
+        return retValue;
+    }
+
+    /**
+     * Added item to the rear of LinkedQueue.
+     *
+     * @param item the item to be added.
+     * @return {@code true} if add successfully.
+     */
+    public boolean enqueue(E item) {
+        Node<E> newNode = new Node<>(item);
+        if (size == 0) {
+            front = rear = newNode;
+        } else {
+            rear.next = newNode;
+            rear = newNode;
+        }
+        size++;
+        return true;
+    }
+
+    /**
+     * Test if this queue is empty or not.
+     *
+     * @return {@code true} if
+     */
+    public boolean empty() {
+        return size == 0;
+    }
+
+    @Override
+    public String toString() {
+        StringJoiner joiner = new StringJoiner(", ", "[", "]");
+        Node<E> temp = front;
+        while (temp != null) {
+            joiner.add(temp.data.toString());
+            System.out.println(temp.data);
+            temp = temp.next;
+        }
+        return joiner.toString();
+    }
+
+    /**
+     * Return the number of elements in this LinkedQueue.
+     *
+     * @return the number of elements in this LinkedQueue.
+     */
+    public int size() {
+        return size;
+    }
+
+    /**
+     * Clear all elements in the LinkedQueue.
+     */
+    public void clear() {
+        front = rear = null;
+        size = 0;
+    }
+}
diff --git a/src/test/java/com/examplehub/datastructures/queue/LinkedQueueTest.java b/src/test/java/com/examplehub/datastructures/queue/LinkedQueueTest.java
@@ -0,0 +1,37 @@
+package com.examplehub.datastructures.queue;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class LinkedQueueTest {
+    @Test
+    void testQueue() throws IllegalAccessException {
+        LinkedQueue<String> queue = new LinkedQueue<>();
+        assertTrue(queue.empty());
+        assertEquals(0, queue.size());
+        assertEquals("[]", queue.toString());
+
+        for (int i = 1; i <= 5; ++i) {
+            queue.enqueue(i + "");
+        }
+        assertEquals(5, queue.size());
+        assertEquals("[1, 2, 3, 4, 5]", queue.toString());
+
+        assertEquals("1", queue.dequeue());
+        assertEquals("2", queue.dequeue());
+        assertEquals("[3, 4, 5]", queue.toString());
+
+        assertTrue(queue.enqueue("1"));
+        assertTrue(queue.enqueue("2"));
+        assertEquals("[3, 4, 5, 1, 2]", queue.toString());
+
+        assertEquals("3", queue.dequeue());
+        assertEquals("4", queue.dequeue());
+
+        queue.clear();
+        assertEquals(queue.size(), 0);
+        assertTrue(queue.empty());
+        assertEquals("[]", queue.toString());
+    }
+}
