We make this observation precise by observing that the To re-sort the entire list, if we start with a sorted list and are But this is a bit inefficient: we shouldn’t need To first insert the new priority and item into the list, and then sort """ if self.is_empty(): raise EmptyPriorityQueueError else: _priority, item = self._items.pop() return itemĪs an exercise, we’ll leave you to show that each of these operationsĪbout PriorityQueue.enqueue? An initial approach might be Raise an EmptyPriorityQueueError when the priority queue is empty. """ return self._items = def dequeue( self) -> Any: """Remove and return the item with the highest priority. """ # Private Instance Attributes: # - _items: a list of the items in this priority queue _items: list] def _init_( self) -> None: """Initialize a new and empty priority queue.""" self._items = def is_empty( self) -> bool: """Return whether this priority queue contains no items. When removing an item from the queue, the highest-priority item is the one that is removed. With this idea, three of the four PriorityQueue methodsĬlass PriorityQueue: """A queue of items that can be dequeued in priority order. Item to be removed from the priority queue. Order), so that the last element in the list is always the next Sorted with respect to priority (breaking ties by insertion Our implementation idea here is to use a private attribute that is a Of which one has the largest priority, and in the case of ties, which Somehow we need to not only store items, but also keep track Unlike with the Stack and Queue ADTs, it is not clear if we can use a """ class EmptyPriorityQueueError( Exception): """Exception raised when calling pop on an empty priority queue.""" def _str_( self) -> str: """Return a string representation of this error.""" return 'You called dequeue on an empty priority queue.' List-based """ def dequeue( self) -> Any: """Remove and return the item with the highest priority. """ def enqueue( self, priority: int, item: Any) -> None: """Add the given item with the given priority to this priority queue. > pq = PriorityQueue() > pq.is_empty() True > pq.enqueue(1, 'hello') > pq.is_empty() False > pq.enqueue(5, 'goodbye') > pq.enqueue(2, 'hi') > pq.dequeue() 'goodbye' """ def _init_( self) -> None: """Initialize a new and empty priority queue.""" def is_empty( self) -> bool: """Return whether this priority queue contains no items. Here is the public interface of a PriorityQueueįrom typing import Any class PriorityQueue: """A collection items that are be removed in priority order. Next chapter, we’ll study an application of priority queues that uses aĭifferent way of representing priorities. Integers, with larger integers representing higher priorities.
For this section, we’ll simply represent priorities as
One subtlety with our definition of this ADT is in how we represent Item with a priority ( enqueue), remove the highest priority Operations: determine whether the priority queue is empty, add an.Data: a collection of items and their priorities.Removed from a Priority Queue in order of their priority, and ties are The Priority Queue ADT is similar to the Queue ADT,Įxcept that every item has some measure of its “priority”. In other words, patients are prioritized based on Life-threatening issues are seen earlier than others, regardless of when Instead, the medical team perform an initial assessment of each patientįor the severity of their illness, and patients with more Room at a hospital does not see patients in the order that they arrive. Restaurant serves customers in a first-in-first-out order, the emergency Current CSC110/111 students should visit the current notes page. NOTE: This is the archived 2022-23 version of these notes, and may be out of date.
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