diff --git a/Sprint-2/implement_linked_list/linked_list.py b/Sprint-2/implement_linked_list/linked_list.py index e69de29..e17b30c 100644 --- a/Sprint-2/implement_linked_list/linked_list.py +++ b/Sprint-2/implement_linked_list/linked_list.py @@ -0,0 +1,47 @@ +class Node: + __slots__ = ("value", "previous", "next") + + def __init__(self, value): + self.value = value + self.previous: "Node | None" = None + self.next: "Node | None" = None + + +class LinkedList: + def __init__(self): + self.head: Node | None = None + self.tail: Node | None = None + + def push_head(self, value) -> Node: + """Add a value to the front of the list. Returns a handle for O(1) removal.""" + node = Node(value) + if self.head is None: + self.head = self.tail = node + else: + node.next = self.head + self.head.previous = node + self.head = node + return node + + def pop_tail(self): + """Remove and return the value at the end of the list.""" + if self.tail is None: + raise IndexError("pop from empty list") + node = self.tail + self.remove(node) + return node.value + + def remove(self, node: Node) -> None: + """Remove a node from the list in O(1) using a handle from push_head""" + if node.previous is not None: + node.previous.next = node.next + else: + self.head = node.next + + if node.next is not None: + node.next.previous = node.previous + else: + self.tail = node.previous + + node.previous = None + node.next = None