Peek Method For Priority Queue

Question

I am implementing a priority queue using a singly sorted linked list. How do I do the peek method? It is supposed to return a copy of the next item in the queue, without removing the item. The next item is the same value that would be returned by the dequeue operation. An item cannot be dequeued from an empty queue.

Would I simply just return a part of my dequeued function or would I do something else??

My Code:

class Node( object ) :
  def __init__( self, cargo = None, next = None ) :
      self.cargo = cargo
      self.next = next

# Creates a new empty unbounded priority queue
class PriorityQueue :


  def __init__( self ) :
      self.length = 0
      self.head = None
      self.last = None

 # Returns a boolean value indicating whether the queue is empty
  def isEmpty( self ) :
      return (self.length == 0)

 # Returns the number of items currently in the queue
 def __len__( self ) :
      return len(self.length)


 # Adds the given item to the queue by inserting it in the proper position 
 # based on the given priority. The new node is appeneded to the end of the
 # linked list
  def enqueue( self, item, priority) :
      newNode = Node(cargo)
      newNode.next = None
      if self.length == 0:
          self.head self.last = newNode
      newNode.next = self.head
      self.head = newNode
      self.last.next = newNode
      self.last = newNode

      temp = self.head
      p = self.head.next
      while p != None :
          if p.cargo > newNode.cargo:
             temp = temp.next
             p = p.next
          break
      newNode.next = temp.next
      temp.next = newNode


 # Removes and returns the next item from the queue, which is the item with 
 # the highest priority. If two or more items have the same priority, those 
 # items are removed in FIFO order. An item cannot be dequeued from an
 # empty queue. The linked list is searched to find the entry with the  
 # highest priority.
  def dequeue( self ) :
      cargo = self.head.cargo
      self.head = self.head.next
      self.length = self.length - 1
      if self.length == 0:
          self.last = None
      return cargo


# Returns a copy of the next item in the queue, without removing the item. 
# The next item is the same value that would be returned by the dequeue 
# operation. An item cannot be dequeued from an empty queue.
  def peek( self ) :

This should help you understand it. http://stackoverflow.com/questions/394809/does-python-have-a-ternary-conditional-operator — Shashank, Apr 15 '15 at 01:15
@Shashank thank you!! Can you take a look to see if the rest of my code looks okay? I very new to Python and trying out programs to get the hang of coding with python — lindsay, Apr 15 '15 at 01:20
Sorry I don't have the time for that...but just keep reading and learning more about Python and testing your code and you will be fine :) — Shashank, Apr 15 '15 at 01:54
stdlib approach: https://stackoverflow.com/questions/16686292/examining-items-in-a-python-queue/16686433#16686433 — n611x007, May 10 '15 at 17:06

Saicharan S M · Accepted Answer · 2015-04-15T01:22:42.387

1

Def Peek():
    if not self.empty():
        return self.head.cargo
    else:
        return None

edited Apr 15 '15 at 01:22

answered Apr 15 '15 at 01:17

Saicharan S M

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is this referring to the dequeue function or the peek function? – lindsay Apr 15 '15 at 01:21
Lindsay I guess you are new to stackoverflow. Here members any specific questions you have. People can't review your code. – Saicharan S M Apr 15 '15 at 03:26

Peek Method For Priority Queue

1 Answers1