stacks.py

# LIFO - last in, first out

# Use the "end" for adding and removing with a list, because O(1)

# class Node:
#     def __init__(self, value):
#         self.value = value
#         self.next = None
#
#
# class Stack:
#     def __init__(self, value):
#         new_node = Node(value)
#         self.top = new_node
#         self.height = 1
#
#     def print_stack(self):
#         temp = self.top
#         while temp is not None:
#             print(temp.value)
#             temp = temp.next
#
#     def push(self, value):
#         new_node = Node(value)
#         if self.height == 0:
#             self.top == new_node
#         else:
#             new_node.next = self.top
#             self.top = new_node
#         self.height += 1
#
#     def pop(self):
#         if self.height == 0:
#             return None
#         temp = self.top
#         self.top = self.top.next
#         temp.next = None
#         self.height -= 1
#         return temp

# Queue: add on one end, remove on another end

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


class Queue:
    def __init__(self, value):
        new_node = Node(value)
        self.first = new_node
        self.last = new_node
        self.length = 1

    def print_queue(self):
        temp = self.first
        while temp is not None:
            print(temp.value)
            temp = temp.next

    def enqueue(self, value):
        new_node = Node(value)
        if self.first is None:
            self.first = new_node
            self.last = new_node
        else:
            self.last.next = new_node
            self.last = new_node
        self.length += 1

    def dequeue(self):
        if self.length == 0:
            return None
        temp = self.first
        if self.length == 1:
            self.first = None
            self.last = None
        else:
            self.first = self.first.next
            temp.next = None
        self.length -= 1
        return temp


my_queue = Queue(1)
my_queue.enqueue(2)
print(my_queue.dequeue())
print(my_queue.dequeue())
print(my_queue.dequeue())