![]() ![]() 1 st Element – Inserting the 4 into an Empty Priority Queue I'll show the min-heap in its tree and array representations in each step. In the following examples, I will show you step by step how to fill a min-heap-based priority queue with the sample values shown above (4, 7, 3, 8, 2, 9, 6, 5, 1). The example in the following section demonstrates the two steps. Step 2 ensures that, at the end of the operation, each element is again less than its children. Step 1 sounds complicated, but in the array representation, it simply means that the new element is placed in the first free position of the array. As long as the parent node of the new element is less than the element itself (which would violate the min-heap rule), we swap the new node with its parent node.If the lowest level is complete, we append the node under the first node of the lowest level.If the lowest level of the tree is not complete, we insert the new element next to the last node of the lowest level.If the tree is empty, we insert the new element as the root.We insert the new element as the last element in the tree, i.e.:.To insert an element into a heap, we proceed as follows: That tells how the peek() operation has to work: it simply has to return the first element of the array.īut how is such a heap constructed? How do enqueue() and dequeue() work? Inserting into the Min-Heap: Sift Up OK, the smallest element is always on the left. Priority Queue Using a Min-Heap – The Algorithm The min-heap of the PriorityQueue created in the example is precisely the one I displayed at the beginning of the article. And if you look closely, you'll see that the numbers are in the same order as in the graphical array representation above. The output of the program is: priorityQueue = Code language: plaintext ( plaintext ) ( "priorityQueue = " + priorityQueue) Code language: Java ( java ) The following lines of code demonstrate this well: PriorityQueue priorityQueue = new PriorityQueue() What you see is the array representation of the min-heap underlying the PriorityQueue. This is why, when you print a Java PriorityQueue as a string, you see the smallest element on the left. In a min-heap, the smallest element is always at the top, i.e., in the array, it is always at the first position. ![]()
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