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GeezerVison is showing github.com — Java/DataStructures/Queues/LinkedQueue.java at master · pythonpeixun/Java

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package DataStructures;
import java.util.NoSuchElementException;
public class LinkedQueue {
class Node {
int data;
Node next;
public Node() {
this(0);
}
public Node(int data) {
this(data, null);
}
public Node(int data, Node next) {
this.data = data;
this.next = next;
}
}
/**
* Front of Queue
*/
private Node front;
/**
* Rear of Queue
*/
private Node rear;
/**
* Size of Queue
*/
private int size;
/**
* Init LinkedQueue
*/
public LinkedQueue() {
front = rear = new Node();
}
/**
* Check if queue is empty
*
* @return <tt>true</tt> if queue is empty, otherwise <tt>false</tt>
*/
public boolean isEmpty() {
return size == 0;
}
/**
* Add element to rear of queue
*
* @param data insert value
* @return <tt>true</tt> if add successfully
*/
public boolean enqueue(int data) {
Node newNode = new Node(data);
rear.next = newNode;
rear = newNode; /* make rear point at last node */
size++;
return true;
}
/**
* Remove element at the front of queue
*
* @return element at the front of queue
*/
public int dequeue() {
if (isEmpty()) {
throw new NoSuchElementException("queue is empty");
}
Node destroy = front.next;
int retValue = destroy.data;
front.next = front.next.next;
destroy = null; /* clear let GC do it's work */
size--;
if (isEmpty()) {
front = rear;
}
return retValue;
}
/**
* Peek element at the front of queue without removing
*
* @return element at the front
*/
public int peekFront() {
if (isEmpty()) {
throw new NoSuchElementException("queue is empty");
}
return front.next.data;
}
/**
* Peek element at the rear of queue without removing
*
* @return element at the front
*/
public int peekRear() {
if (isEmpty()) {
throw new NoSuchElementException("queue is empty");
}
return rear.data;
}
/**
* Return size of queue
*
* @return size of queue
*/
public int size() {
return size;
}
/**
* Clear all nodes in queue
*/
public void clear() {
while (!isEmpty()) {
dequeue();
}
}
@Override
public String toString() {
if (isEmpty()) {
return "[]";
}
StringBuilder builder = new StringBuilder();
Node cur = front.next;
builder.append("[");
while (cur != null) {
builder.append(cur.data).append(", ");
cur = cur.next;
}
builder.replace(builder.length() - 2, builder.length(), "]");
return builder.toString();
}
/* Driver Code */
public static void main(String[] args) {
LinkedQueue queue = new LinkedQueue();
assert queue.isEmpty();
queue.enqueue(1); /* 1 */
queue.enqueue(2); /* 1 2 */
queue.enqueue(3); /* 1 2 3 */
System.out.println(queue); /* [1, 2, 3] */
assert queue.size() == 3;
assert queue.dequeue() == 1;
assert queue.peekFront() == 2;
assert queue.peekRear() == 3;
queue.clear();
assert queue.isEmpty();
System.out.println(queue); /* [] */
}
}
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