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154. Priority Queue in Data Structure
Earlier in we have seen MinHeap and MaxHeap Implementation. Priority Queue is its builtin implementation in Java.
In this article, we will see how to perform MinHeap and MaxHeap using Priority Queue.
Brief:
A priority queue is an abstract data type where each element has a “priority” assigned to it. So the element with the higher priority is served before the other elements. Click here to know in detail about maxHeap and minHeap. (Source: Wiki)
Return Type  Method  Description 
boolean  offer(E e)  Inserts the specified element into this priority queue. 
E  peek()  Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty. 
E  poll()  Retrieves and removes the head of this queue, or returns null if this queue is empty. 
int  size()  Returns the number of elements in this collection. 
void  clear()  Removes all of the elements from this priority queue. 
boolean  contains(Object o)  Returns true if this queue contains the specified element. 
Iterator<E>  iterator()  Returns an iterator over the elements in this queue. 
boolean  remove(Object o)  Removes a single instance of the specified element from this queue, if it is present. 
Comparator<? super E>  comparator()  Returns the comparator used to order the elements in this queue, or null if this queue is sorted according to the natural ordering of its elements. 
MinHeap using Priority Queue:
Output:
Output: [1, 4, 2, 9, 6, 3, 8] Min Element in the Priority Queue: 1 Min Element in the Priority Queue: 2 Min Element in the Priority Queue: 3 Priority Queue Size: 4
MaxHeap using Priority Queue:
This gets a bit tricky here. By default, the Priority Queue works as minHeap. To implement the maxHeap we need to change the way the priority queue works internally by overriding the Comparator.
Output:
Output: [9, 6, 8, 1, 4, 2, 3] Max Element in the Priority Queue: 9 Max Element in the Priority Queue: 8 Max Element in the Priority Queue: 6 Priority Queue Size: 4
Reference : https://docs.oracle.com/javase/7/docs/api/java/util/PriorityQueue.html