linked_lists.py

class ListNode:
    def __init__(self, value, next):
        self.value = value
        self.next = next

class LinkedList:
    def __init__(self):
        self.head = None

def print_list_values(the_list):
    aux = the_list.head
    while aux != None:
        print(aux.value)
        aux = aux.next

def insert_at_end(the_list, the_node):
    # Two pointers, previous pointer and aux pointer
    prev = None
    aux = the_list.head

    while aux != None:
        prev = aux
        aux = aux.next 

    if prev == None:
        the_list.head = the_node
    else:
        prev.next = the_node

def insert_at_beginning(the_list, the_node):
    the_node.next = the_list.head
    the_list.head = the_node

def insert_at_pos(the_list, the_node, pos):
    prev = None
    aux = the_list.head
    idx = 0

    while aux != None and idx < pos:
        prev = aux
        aux = aux.next
        idx = idx + 1

    if prev == None:
        the_list.head = the_node
    else:
        prev.next = the_node

    the_node.next = aux

def remove_beginning(the_list):
    aux = the_list.head
    the_list.head = aux.next
    return aux

def remove_end(the_list):
    aux = the_list.head
    prev = None

    while aux.next != None:
        prev = aux
        aux = aux.next

    if prev == None:
        result = the_list.head
        the_list.head = None
    else:
        result = prev.next
        prev.next = None

    return result

my_new_list = LinkedList()

new_node1 = ListNode(42, None)
new_node2 = ListNode(64, None)
new_node3 = ListNode(99, None)
new_node4 = ListNode(23, None)

insert_at_end(my_new_list, new_node1)
insert_at_end(my_new_list, new_node2)
insert_at_beginning(my_new_list, new_node3)
insert_at_pos(my_new_list, new_node4, 1)

print_list_values(my_new_list)

remove_beginning(my_new_list)
remove_end(my_new_list)

print()
print_list_values(my_new_list)