Queue Using LL.py

"""
--------------------------------------------  Queue Using LL ----------------------------------------------

You need to implement a Queue class using linked list.
All the required data members should be private.

Implement the following public functions :

1. Constructor -
    Initialises the data members.

2. enqueue :
    This function should take one argument of type T and has return type void. This function should insert 
    an element in the queue. Time complexity should be O(1).

3. dequeue :
    This function takes no input arguments and has return type T. This should removes the first element 
    which is entered and return that element as an answer. Time complexity should be O(1).

4. front :
    This function takes no input arguments and has return type T. This should return the first element 
    which is entered and return that element as an answer. Time complexity should be O(1).

5. size :
    Return the size of stack i.e. count of elements which are present ins stack right now. Time complexity 
    should be O(1).

6. isEmpty :
    Checks if the queue is empty or not. Return true or false.

"""


class Node:
    def __init__(self,data):
        self.data = data
        self.next = None
        
class QueueUsingLL:
  
### Implement These Functions Here    
    def __init__(self):
        self.__head=None
        self.__tail=None
        self.__count=0
        
    def enqueue(self,data):
        newNode=Node(data)
        if self.__head is None:
            self.__head=newNode
        else:
            self.__tail.next=newNode
        self.__tail=newNode
        self.__count=self.__count+1
        
        
    def dequeue(self):
        if self.__head is None:
            return 0
        data=self.__head.data
        self.__head=self.__head.next
        self.__count=self.__count-1
        return data
        
    
    def front(self):
        if self.__head is None:
            return 0
        data=self.__head.data
        return data
        
        
    def isEmpty(self):
        return self.size()==0
       
    
    def getSize(self):
        return self.__count

    
q = QueueUsingLL()
li = [int(ele) for ele in input().split()]
i=0
while i<len(li):
    choice = li[i]
    if choice == -1:
        break
    elif choice == 1:
        q.enqueue(li[i+1])
        i+=1
    elif choice == 2:
        ans = q.dequeue()
        if ans!=0:
            print(ans)
        else:
            print(-1)
    elif choice == 3:
        ans = q.front()
        if ans!=0:
            print(ans)
        else:
            print(-1)
    elif choice == 4:
        print(q.getSize())
    elif choice == 5:
        if(q.isEmpty()):
            print('true')
        else:
            print('false')
    i+=1