How do I use a PriorityQueue?

A PriorityQueue is a queue data structure that manages elements by priority. In Java, you can use the java.util.PriorityQueue class to create a min-heap-based priority queue, which pops the element with the lowest priority first.

Here's an example of how to create a PriorityQueue and add elements to it:

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import java.util.PriorityQueue;

// Create a priority queue
PriorityQueue<Integer> pq = new PriorityQueue<>();

// Add an element with a priority of 10
pq.add(10);

// Add an element with a priority of 5
pq.add(5);

// Add an element with a priority of 1
pq.add(1);

// The queue now looks like this:
// [1, 5, 10]

To pop an element off the queue, use the poll() method:

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// Pop the element with the lowest priority (i.e., 1)
System.out.println(pq.poll());  // Output: 1

// Pop the element with the next lowest priority (i.e., 5)
System.out.println(pq.poll());  // Output: 5

// Pop the element with the highest priority (i.e., 10)
System.out.println(pq.poll());  // Output: 10

// The queue is now empty

You can also initialize a PriorityQueue directly from a collection, which automatically arranges the elements into a heap:

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import java.util.Arrays;
import java.util.List;
import java.util.PriorityQueue;

// Convert a regular list into a priority queue
List<Integer> list = Arrays.asList(10, 5, 1);
PriorityQueue<Integer> pq = new PriorityQueue<>(list);

// The queue is now a heap
System.out.println(pq);  // Output: [1, 5, 10]

By default, Java's PriorityQueue is a min-heap. To create a max-heap (where the highest priority element is popped first), pass Collections.reverseOrder() to the constructor:

import java.util.Collections;
import java.util.PriorityQueue;

PriorityQueue<Integer> maxPq = new PriorityQueue<>(Collections.reverseOrder());
maxPq.add(10);
maxPq.add(5);
maxPq.add(1);
System.out.println(maxPq.poll());  // Output: 10

I hope this helps! Let me know if you have any questions.