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PriorityQueues.java
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123 lines (113 loc) · 2.56 KB
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/**
* This class implements a PriorityQueue.
*
* A priority queue adds elements into positions based on their priority.
* So the most important elements are placed at the front/on the top.
* In this example I give numbers that are bigger, a higher priority.
* Queues in theory have no fixed size but when using an array
* implementation it does.
*
* @author Unknown
*
*/
class PriorityQueue{
/** The max size of the queue */
private int maxSize;
/** The array for the queue */
private int[] queueArray;
/** How many items are in the queue */
private int nItems;
/**
* Constructor
*
* @param size Size of the queue
*/
public PriorityQueue(int size){
maxSize = size;
queueArray = new int[size];
nItems = 0;
}
/**
* Inserts an element in it's appropriate place
*
* @param value Value to be inserted
*/
public void insert(int value){
if(nItems == 0){
queueArray[0] = value;
}
else{
int j = nItems;
while(j > 0 && queueArray[j-1] > value){
queueArray[j] = queueArray[j-1]; //Shifts every element up to make room for insertion
j--;
}
queueArray[j] = value; //Once the correct position is found the value is inserted
}
nItems++;
}
/**
* Remove the element from the front of the queue
*
* @return The element removed
*/
public int remove(){
return queueArray[--nItems];
}
/**
* Checks what's at the front of the queue
*
* @return element at the front of the queue
*/
public int peek(){
return queueArray[nItems-1];
}
/**
* Returns true if the queue is empty
*
* @return true if the queue is empty
*/
public boolean isEmpty(){
return(nItems == 0);
}
/**
* Returns true if the queue is full
*
* @return true if the queue is full
*/
public boolean isFull(){
return(nItems == maxSize);
}
/**
* Returns the number of elements in the queue
*
* @return number of elements in the queue
*/
public int getSize(){
return nItems;
}
}
/**
* This class implements the PriorityQueue class above.
*
* @author Unknown
*
*/
public class PriorityQueues{
/**
* Main method
*
* @param args Command Line Arguments
*/
public static void main(String args[]){
PriorityQueue myQueue = new PriorityQueue(4);
myQueue.insert(10);
myQueue.insert(2);
myQueue.insert(5);
myQueue.insert(3);
//[2, 3, 5, 10] Here higher numbers have higher priority, so they are on the top
for(int i = 3; i>=0; i--)
System.out.print(myQueue.remove() + " "); //will print the queue in reverse order [10, 5, 3, 2]
//As you can see, a Priority Queue can be used as a sorting algotithm
}
}