![]() is_empty Check whether the queue is empty. remove Remove and return an item from the queue. Again, the interface is: _init_ Initialize a new empty queue. The Priority Queue ADT has the same interface as the Queue ADT, but different Convince yourself that this method preserves ![]() Length should be the number of nodes in the queue, and the last node should There are two invariants for a properly formed Queue object. We can identify the last node because its next attribute is None. Otherwise, we traverse the list to the last node and tack the new node on theĮnd. We want to insert new items at the end of the list. The methods is_empty and remove are identical to the LinkedList length += 1 def remove ( self ): cargo = self. head = node else : # Find the last node in the list last = self. head is None : # If list is empty the new node goes first self. length = 0 def insert ( self, cargo ): node = Node ( cargo ) if self. head = None def is_empty ( self ): return self. Theĭifference is in the semantics of the operations: a queue uses the FIFO policy Īnd a priority queue (as the name suggests) uses the priority queueing policy.Ĭlass Queue : def _init_ ( self ): self. The Queue ADT and the Priority Queue ADT have the same set of operations. Not all queueing policies are fair, but fairness is in the eye of the beholder. Many groceries the person has or how important the person is. We say this is the most general policyīecause the priority can be based on anything: what time a flight leaves how General queueing policy is priority queueing, in which each person isĪssigned a priority and the person with the highest priority goes first, Simplest queueing policy is called “First in, First out”, FIFO for short. The rule that determines who goes next is called the queueing policy. Person might let someone with only a few items go in front of them. Sometimes taken from the middle of the queue. At airports, peoples whose flights are leaving soon are In mostĬases, the first person in line is the next one to be served. ![]() In real life,Ī queue is a line of people waiting for something. Prio_queue.put((1, time.This chapter presents two ADTs: the Queue and the Priority Queue. Prio_queue.put((1, time.time(), 'This thing would come after Some Thing if we sorted by this text entry')) Prio_queue.put((2, time.time(), 'super blah')) Hopefully this helps as another example of how you might get the ordering you're after. I added a short sleep so this simple example works out in a reasonable way. I say fake because it's only approximately FIFO as entries that are added very close in time to one another may not come out exactly FIFO. Here's what it looks like if you use a timestamp to fake FIFO as a secondary priority using a date. Output 1.3 - This thing would come after Some Thing if we didn't add a secondary priority Prio_queue.put((1, 3, 'This thing would come after Some Thing if we sorted by this text entry')) Using a datetime value in the second position is a pretty trivial change, but feel free to poke me in comments if you're not able to get it working. Here's some example code with just a secondary numeric priority. ![]() A date/time priority would give you a priority queue that falls back to a FIFIO queue when you have multiple items with the same priority. Just use the second item of the tuple as a secondary priority if a alphanumeric sort on your string data isn't appropriate. ![]()
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