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132 lines
2.7 KiB
Plaintext
132 lines
2.7 KiB
Plaintext
/* $Id$ */
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/**
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* Binary Heap.
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* Peek and Pop always return the current lowest value in the list.
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* Sort is done on insertion and on deletion.
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*/
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class BinaryHeap
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{
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_queue = null;
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_count = 0;
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constructor()
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{
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_queue = [];
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}
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/**
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* Insert a new entry in the list.
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* The complexity of this operation is O(ln n).
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* @param item The item to add to the list.
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* @param priority The priority this item has.
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*/
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function Insert(item, priority);
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/**
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* Pop the first entry of the list.
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* This is always the item with the lowest priority.
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* The complexity of this operation is O(ln n).
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* @return The item of the entry with the lowest priority.
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*/
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function Pop();
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/**
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* Peek the first entry of the list.
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* This is always the item with the lowest priority.
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* The complexity of this operation is O(1).
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* @return The item of the entry with the lowest priority.
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*/
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function Peek();
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/**
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* Get the amount of current items in the list.
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* The complexity of this operation is O(1).
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* @return The amount of items currently in the list.
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*/
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function Count();
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/**
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* Check if an item exists in the list.
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* The complexity of this operation is O(n).
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* @param item The item to check for.
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* @return True if the item is already in the list.
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*/
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function Exists(item);
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};
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function BinaryHeap::Insert(item, priority)
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{
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/* Append dummy entry */
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_queue.append(0);
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_count++;
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local hole;
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/* Find the point of insertion */
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for (hole = _count - 1; hole > 0 && priority <= _queue[hole / 2][1]; hole /= 2)
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_queue[hole] = _queue[hole / 2];
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/* Insert new pair */
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_queue[hole] = [item, priority];
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return true;
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}
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function BinaryHeap::Pop()
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{
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if (_count == 0) return null;
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local node = _queue[0];
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/* Remove the item from the list by putting the last value on top */
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_queue[0] = _queue[_count - 1];
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_queue.pop();
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_count--;
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/* Bubble down the last value to correct the tree again */
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_BubbleDown();
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return node[0];
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}
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function BinaryHeap::Peek()
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{
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if (_count == 0) return null;
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return _queue[0][0];
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}
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function BinaryHeap::Count()
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{
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return _count;
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}
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function BinaryHeap::Exists(item)
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{
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/* Brute-force find the item (there is no faster way, as we don't have the priority number) */
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foreach (node in _queue) {
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if (node[0] == item) return true;
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}
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return false;
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}
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function BinaryHeap::_BubbleDown()
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{
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if (_count == 0) return;
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local hole = 1;
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local tmp = _queue[0];
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/* Start switching parent and child until the tree is restored */
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while (hole * 2 < _count + 1) {
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local child = hole * 2;
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if (child != _count && _queue[child][1] <= _queue[child - 1][1]) child++;
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if (_queue[child - 1][1] > tmp[1]) break;
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_queue[hole - 1] = _queue[child - 1];
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hole = child;
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}
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/* The top value is now at his new place */
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_queue[hole - 1] = tmp;
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}
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