class List_Node:
    # self.data
    # self.next

    # constructor
    # O(1) time
    def __init__(self, data):
        self.data = data
        self.next = None

    # Called when printing the object
    # O(1) time
    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
    # O(n) runtime    

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


def print_rec(L):
    # Runtime O(n)
    # 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
    # Runtime proportional to length of list: O(n)

    ### 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)
    return L # nothing has changed


def list_search(L,x):
    # Runtime: O(n)  for worst-case input
    current = L
    while current!=None:
        if current.data==x:
            return current
        current=current.next
    return None

def list_remove(L,x):
    # Removes item x from list
    # Runtime O(n)  in the worst-case

    # Special case for first element
    if L.data==x:
        L = L.next # Updating front reference
        return L

    prev = L
    current = L.next
    while current!=None and current.data!=x:
        prev=current
        current=current.next

    # Remove node with data element x
    if current!=None and current.data==x:
    # if current.data==x:
        prev.next = current.next

    return L # Nothing has changed, but need to return something    
        

 def list_remove2(L,x):
    # Removes item x from list
    # Runtime O(n)  in the worst-case

    # Special case for first element
    if L.data==x:
        L = L.next # Updating front reference
        
    else: # Rest of list
        prev = L
        current = L.next
        while current!=None and current.data!=x:
            prev=current
            current=current.next

        # Remove node with data element x
        if current!=None and current.data==x:
        # if current.data==x:
            prev.next = current.next

    return L # Nothing has changed, but need to return something    
        

# 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)
print
mylist = list_remove(mylist,5)
print "After removing 5:"
print_rec(mylist)
print
mylist = list_remove(mylist,0)
print "After removing 0:"
print_rec(mylist)