Tag: priority-queue

How to Peek the Lowest elements from a List of sorted Streams continously

I started learning about Java Stream, and I am wondering is it possible to only peek the first element of the stream without retrieving it. For example, I have multiple streams, and each of them have integers that are sorted in non-decreasing order, and I want to get a sorted list of all integers, so I’…

Java – Use PriorityQueue sort list but have empty list

java priority-queue

This is my solution for leetcode 759. Employee Free Time, but it has index out of boundary issue that i don’t understand. I got “index 0 out of bounds for length 0” exception. The test case i used is ‘[[[1,2]],[[1,3]],[[4,10]]]’ and this is the output: I only have 3 lists and bas…

Is there any efficient algorithm for traversing a Heap-Based Priority Queue?

algorithm heap iterator java priority-queue

I have implemented a Heap-Based Priority Queue in Java but my challenge now is implementing an efficient Iterator that has a definite (increasing or decreasing) order of traversal. Is there any algorithm that does this at constant auxiliary space and time complexity of O(n)? The O(nlogn) is quite trivial. Als…

Java PriorityQueue: how to heapify a Collection with a custom Comparator?

heap java priority-queue

For example, given a List of Integer List<Integer> list = Arrays.asList(5,4,5,2,2), how can I get a maxHeap from this List in O(n) time complexity? The naive method: However, the time complexity is O(nlogn). We can trigger the heapify method by using the following constructor: The time complexity is O(n…

Is PriorityQueue a FIFO Queue?

java priority-queue

PriorityQueue implements Queue, but is PriorityQueue a FIFO data structure like Queue? Answer From the Queue interface: Queues typically, but do not necessarily, order elements in a FIFO (first-in-first-out) manner. Among the exceptions are priority queues, which order elements according to a supplied compara…

Change priorityQueue to max priorityqueue

collections java priority-queue

I have priority queue in Java of Integers: When I call pq.poll() I get the minimum element. Question: how to change the code to get the maximum element? Answer How about like this: The Collections.reverseOrder() provides a Comparator that would sort the elements in the PriorityQueue in a the oposite order to …