123 lines
2.6 KiB
Java
123 lines
2.6 KiB
Java
/**
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* This class implements a PriorityQueue.
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*
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* A priority queue adds elements into positions based on their priority.
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* So the most important elements are placed at the front/on the top.
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* In this example I give numbers that are bigger, a higher priority.
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* Queues in theory have no fixed size but when using an array
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* implementation it does.
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*
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* @author Unknown
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*
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*/
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class PriorityQueue{
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/** The max size of the queue */
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private int maxSize;
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/** The array for the queue */
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private int[] queueArray;
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/** How many items are in the queue */
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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 queue
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*/
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public PriorityQueue(int size){
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maxSize = size;
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queueArray = new int[size];
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nItems = 0;
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}
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/**
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* Inserts an element in it's appropriate place
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*
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* @param value Value to be inserted
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*/
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public void insert(int value){
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if(nItems == 0){
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queueArray[0] = value;
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}
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else{
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int j = nItems;
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while(j > 0 && queueArray[j-1] > value){
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queueArray[j] = queueArray[j-1]; //Shifts every element up to make room for insertion
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j--;
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}
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queueArray[j] = value; //Once the correct position is found the value is inserted
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}
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nItems++;
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}
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/**
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* Remove the element from the front of the queue
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*
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* @return The element removed
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*/
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public int remove(){
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return queueArray[--nItems];
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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 peek(){
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return queueArray[nItems-1];
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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 implements the PriorityQueue class above.
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*
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* @author Unknown
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*
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*/
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public class PriorityQueues{
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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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PriorityQueue myQueue = new PriorityQueue(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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//[2, 3, 5, 10] Here higher numbers have higher priority, so they are on the top
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for(int i = 3; i>=0; i--)
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System.out.print(myQueue.remove() + " "); //will print the queue in reverse order [10, 5, 3, 2]
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//As you can see, a Priority Queue can be used as a sorting algotithm
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}
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} |