class List_Node:
    # self.data
    # self.next

    # constructor
    def __init__(self, data):
        self.data = data
        self.next = None

    # Called when printing the object
    def __str__(self):
        return str(self.data)


    def print_linked_list_pretty(self):
        # self is front node of list
        # Takes time proportional to length of list: O(n)

        current=self
        while(current!=None):
            print current, "->",
            current = current.next
        print "None"    

def print_linked_list(L):
    # L is front node of list

    current=L
    while(current!=None):
        print current # prints current.__str__()
        current = current.next


def print_rec(L):
    # Base case
    # Stop when we hit None
    if L==None:
        print "None"

    else:
        # Recursive case
        print L.data, "->",
        print_rec(L.next)

def add(L,x):
    # Add new element x to front of list L
    # Runtime O(1)

    newnode = List_Node(x) # (1)
    newnode.next=L         # (1)
    # L=newnode
    # print_rec(L)
    return newnode # (2) New front of list

def append(L,x):
    # Add  new element x to the end of list L

    ### Need to deal with case when L==None
    if L==None:
        return List_Node(x)

    current = L
    while(current.next!=None):   #(1)
        current = current.next   #(1)

    current.next = List_Node(x)  # (2)    

        
    
# Create L: 'a'->'b'->'c'->'d'->None
L=List_Node('a') # L: 'a' -> None
L.next=List_Node('b')
L.next.next=List_Node('c')
L.next.next.next=List_Node('d')

L.print_linked_list_pretty()
print_rec(L)
print_rec(None)


# Create list 0->1->2->3->...->n-1->None
n=20

mylist = List_Node(0)
current = mylist
for i in range(1,n):
    current.next = List_Node(i)
    current = current.next

print_rec(mylist)

mylist=add(mylist,42)
print_rec(mylist)
print
mylist=append(mylist,100)
print_rec(mylist)

otherList=None
otherList=append(otherList,100)
print_rec(otherList)