diff --git a/bin/ai/library/queue/priority_queue/main.nut b/bin/ai/library/queue/priority_queue/main.nut new file mode 100644 --- /dev/null +++ b/bin/ai/library/queue/priority_queue/main.nut @@ -0,0 +1,115 @@ +/* $Id$ */ + +/** + * Priority Queue. + * Peek and Pop always return the current lowest value in the list. + * Sort is done on insertion only. + */ +class PriorityQueue +{ + _queue = null; + _count = 0; + + constructor() + { + _count = 0; + _queue = []; + } + + /** + * Insert a new entry in the list. + * The complexity of this operation is O(n). + * @param item The item to add to the list. + * @param priority The priority this item has. + */ + function Insert(item, priority); + + /** + * Pop the first entry of the list. + * This is always the item with the lowest priority. + * The complexity of this operation is O(1). + * @return The item of the entry with the lowest priority. + */ + function Pop(); + + /** + * Peek the first entry of the list. + * This is always the item with the lowest priority. + * The complexity of this operation is O(1). + * @return The item of the entry with the lowest priority. + */ + function Peek(); + + /** + * Get the amount of current items in the list. + * The complexity of this operation is O(1). + * @return The amount of items currently in the list. + */ + function Count(); + + /** + * Check if an item exists in the list. + * The complexity of this operation is O(n). + * @param item The item to check for. + * @return True if the item is already in the list. + */ + function Exists(item); +}; + +function PriorityQueue::Insert(item, priority) +{ + /* Append dummy entry */ + _queue.append(0); + _count++; + + local i; + /* Find the point of insertion */ + for (i = _count - 2; i >= 0; i--) { + if (priority > _queue[i][1]) { + /* All items bigger move one place to the right */ + _queue[i + 1] = _queue[i]; + } else if (item == _queue[i][0]) { + /* Same item, ignore insertion */ + return false; + } else { + /* Found place to insert at */ + break; + } + } + /* Insert new pair */ + _queue[i + 1] = [item, priority]; + + return true; +} + +function PriorityQueue::Pop() +{ + if (_count == 0) return null; + + local node = _queue.pop(); + _count--; + + return node[0]; +} + +function PriorityQueue::Peek() +{ + if (_count == 0) return null; + + return _queue[_count - 1][0]; +} + +function PriorityQueue::Count() +{ + return _count; +} + +function PriorityQueue::Exists(item) +{ + /* Brute-force find the item (there is no faster way, as we don't have the priority number) */ + foreach (node in _queue) { + if (node[0] == item) return true; + } + + return false; +}