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