deque-linked.py

# Copyright (C) Deepali Srivastava - All Rights Reserved
# This code is part of DSA course available on CourseGalaxy.com  

class EmptyQueueError(Exception):
    pass

class Node:
    def __init__(self,value):
        self.info = value 
        self.prev = None
        self.next = None
        
class Deque:

    def __init__(self):
        self.front = None
        self.rear = None
    
    def is_empty(self):
         return self.front == None
    
    def size(self):
        count = 0
        p = self.front
        while p is not None:
            count+=1
            p = p.next
        return count
    
    def insert_front(self, item):
        temp = Node(item)
        if self.is_empty():
            self.front = self.rear = temp
        else:
            temp.next = self.front
            self.front.prev = temp
            self.front = temp
        
    def insert_rear(self, item):
        temp = Node(item)
        if self.is_empty():
            self.front = self.rear = temp
        else:
            self.rear.next = temp
            temp.prev = self.rear
        
        self.rear = temp
        
    def delete_front(self):
        if self.is_empty():  
           raise EmptyQueueError("Queue is empty")

        x = self.front.info
        if self.front.next is None: # list has only one node
            self.front = self.rear = None
        else:
            self.front = self.front.next
            self.front.prev = None
        return x
       
    def delete_rear(self):
        if self.is_empty():   
           raise EmptyQueueError("Queue is empty")

        x = self.rear.info
        if self.front.next is None:  # list has only one node
            self.front = self.rear = None
        else:
            self.rear = self.rear.prev
            self.rear.next = None
        return x
    
    def first(self):
        if self.is_empty():  
           raise EmptyQueueError("Queue is empty")

        return self.front.info

    def last(self):
        if self.is_empty():  
           raise EmptyQueueError("Queue is empty")

        return self.rear.info

    def display(self):
        if self.front is None:
            print("List is empty")
            return

        print("List is : ")
        p = self.front
        while p is not None:
            print(p.info, "  ", end='')
            p = p.next
        print()
     
        
####################################################################

if __name__ == "__main__":
    qu = Deque()

    while True:
        print("1.Insert at the front end")
        print("2.Insert at the rear end")
        print("3.Delete from front end")
        print("4.Delete from rear end")
        print("5.Display first element")
        print("6.Display last element")
        print("7.Display")
        print("8.Size")
        print("9.Quit")
             
        choice = int(input("Enter your choice : "))

        if choice == 1:
            x=int(input("Enter the element : "))
            qu.insert_front(x)
        elif choice== 2:
            x=int(input("Enter the element : "))
            qu.insert_rear(x)
        elif choice == 3:
            x = qu.delete_front()
            print("Element deleted from front end is  ", x)
        elif choice == 4:
            x = qu.delete_rear()
            print("Element deleted from rear end is  ", x)
        elif choice == 5:
            print("First element is  ", qu.first())
        elif choice == 6:
            print("Last element is  ", qu.last())
        elif choice == 7:
            qu.display()
        elif choice == 8:
            print("Size of queue " , qu.size())
        elif choice == 9:
            break
        else:
            print("Wrong choice")
        print()