159 lines
3.6 KiB
Java
159 lines
3.6 KiB
Java
package DataStructures.Queues;
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/**
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* This implements Queues by using the class Queue.
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* <p>
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* A queue data structure functions the same as a real world queue.
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* The elements that are added first are the first to be removed.
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* New elements are added to the back/rear of the queue.
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*
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* @author Unknown
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*/
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class Queue {
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/**
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* Max size of the queue
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*/
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private int maxSize;
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/**
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* The array representing the queue
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*/
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private int[] queueArray;
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/**
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* Front of the queue
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*/
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private int front;
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/**
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* Rear of the queue
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*/
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private int rear;
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/**
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* How many items are in the queue
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*/
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private int nItems;
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/**
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* Constructor
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*
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* @param size Size of the new queue
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*/
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public Queue(int size) {
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maxSize = size;
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queueArray = new int[size];
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front = 0;
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rear = -1;
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nItems = 0;
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}
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/**
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* Inserts an element at the rear of the queue
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*
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* @param x element to be added
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* @return True if the element was added successfully
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*/
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public boolean insert(int x) {
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if (isFull())
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return false;
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if (rear == maxSize - 1) // If the back of the queue is the end of the array wrap around to the front
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rear = -1;
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rear++;
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queueArray[rear] = x;
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nItems++;
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return true;
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}
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/**
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* Remove an element from the front of the queue
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*
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* @return the new front of the queue
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*/
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public int remove() { // Remove an element from the front of the queue
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if (isEmpty()) {
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System.out.println("Queue is empty");
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return -1;
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}
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int temp = queueArray[front];
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front++;
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if (front == maxSize) //Dealing with wrap-around again
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front = 0;
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nItems--;
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return temp;
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}
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/**
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* Checks what's at the front of the queue
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*
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* @return element at the front of the queue
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*/
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public int peekFront() {
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return queueArray[front];
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}
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/**
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* Checks what's at the rear of the queue
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*
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* @return element at the rear of the queue
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*/
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public int peekRear() {
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return queueArray[rear];
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}
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/**
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* Returns true if the queue is empty
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*
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* @return true if the queue is empty
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*/
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public boolean isEmpty() {
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return (nItems == 0);
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}
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/**
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* Returns true if the queue is full
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*
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* @return true if the queue is full
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*/
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public boolean isFull() {
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return (nItems == maxSize);
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}
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/**
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* Returns the number of elements in the queue
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*
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* @return number of elements in the queue
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*/
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public int getSize() {
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return nItems;
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}
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}
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/**
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* This class is the example for the Queue class
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*
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* @author Unknown
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*/
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public class Queues {
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/**
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* Main method
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*
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* @param args Command line arguments
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*/
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public static void main(String args[]) {
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Queue myQueue = new Queue(4);
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myQueue.insert(10);
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myQueue.insert(2);
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myQueue.insert(5);
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myQueue.insert(3);
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// [10(front), 2, 5, 3(rear)]
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System.out.println(myQueue.isFull()); // Will print true
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myQueue.remove(); // Will make 2 the new front, making 10 no longer part of the queue
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// [10, 2(front), 5, 3(rear)]
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myQueue.insert(7); // Insert 7 at the rear which will be index 0 because of wrap around
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// [7(rear), 2(front), 5, 3]
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System.out.println(myQueue.peekFront()); // Will print 2
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System.out.println(myQueue.peekRear()); // Will print 7
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}
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}
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