Java/DataStructures/Queues/LinkedQueue.java at master · primary-code-test/Java · GitHub

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package DataStructures.Queues;

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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