From 602505df7e412a472ae614cf77d3330f38a90259 Mon Sep 17 00:00:00 2001 From: RahwaZeslusHaile Date: Wed, 25 Feb 2026 23:27:32 +0000 Subject: [PATCH 1/4] Implement doubly-linked list with O(1) operations --- Sprint-2/implement_linked_list/linked_list.py | 57 +++++++++++++++++++ 1 file changed, 57 insertions(+) diff --git a/Sprint-2/implement_linked_list/linked_list.py b/Sprint-2/implement_linked_list/linked_list.py index e69de29..38cd0df 100644 --- a/Sprint-2/implement_linked_list/linked_list.py +++ b/Sprint-2/implement_linked_list/linked_list.py @@ -0,0 +1,57 @@ +class Node: + def __init__(self, value): + self.value = value + self.next = None + self.previous = None + + +class LinkedList: + def __init__(self): + self.head = None + self.tail = None + + def push_head(self, value): + new_node = Node(value) + + if self.head is None: + self.head = new_node + self.tail = new_node + else: + new_node.next = self.head + self.head.previous = new_node + self.head = new_node + + return new_node + + def pop_tail(self): + + if self.tail is None: + raise IndexError("pop_tail from empty linked list") + + value = self.tail.value + + if self.head == self.tail: + self.head = None + self.tail = None + else: + self.tail = self.tail.previous + self.tail.next = None + + return value + + def remove(self, node): + if node is None: + raise ValueError("Cannot remove None node") + + if node == self.head == self.tail: + self.head = None + self.tail = None + elif node == self.head: + self.head = node.next + self.head.previous = None + elif node == self.tail: + self.tail = node.previous + self.tail.next = None + else: + node.previous.next = node.next + node.next.previous = node.previous \ No newline at end of file From 071bc289a4578e7b40704308347fe6712de8a3be Mon Sep 17 00:00:00 2001 From: RahwaZeslusHaile Date: Mon, 2 Mar 2026 16:45:48 +0000 Subject: [PATCH 2/4] Fix: Set node.next and node.previous to None after removal --- Sprint-2/implement_linked_list/linked_list.py | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/Sprint-2/implement_linked_list/linked_list.py b/Sprint-2/implement_linked_list/linked_list.py index 38cd0df..2efb287 100644 --- a/Sprint-2/implement_linked_list/linked_list.py +++ b/Sprint-2/implement_linked_list/linked_list.py @@ -54,4 +54,7 @@ def remove(self, node): self.tail.next = None else: node.previous.next = node.next - node.next.previous = node.previous \ No newline at end of file + node.next.previous = node.previous + + node.next = None + node.previous = None \ No newline at end of file From 9135980be298b087fada0c79e90c0a4023193c9b Mon Sep 17 00:00:00 2001 From: RahwaZeslusHaile Date: Mon, 2 Mar 2026 21:22:21 +0000 Subject: [PATCH 3/4] Refactor: Delegate pop_tail to remove, add type hints and docstrings --- Sprint-2/implement_linked_list/linked_list.py | 53 +++++++++++-------- 1 file changed, 30 insertions(+), 23 deletions(-) diff --git a/Sprint-2/implement_linked_list/linked_list.py b/Sprint-2/implement_linked_list/linked_list.py index 2efb287..b5f94d7 100644 --- a/Sprint-2/implement_linked_list/linked_list.py +++ b/Sprint-2/implement_linked_list/linked_list.py @@ -1,18 +1,22 @@ +from typing import Optional, Iterator + + class Node: + def __init__(self, value): self.value = value - self.next = None - self.previous = None + self.next: Optional["Node"] = None + self.previous: Optional["Node"] = None class LinkedList: def __init__(self): - self.head = None - self.tail = None + self.head: Optional[Node] = None + self.tail: Optional[Node] = None - def push_head(self, value): + def push_head(self, value) -> Node: new_node = Node(value) - + if self.head is None: self.head = new_node self.tail = new_node @@ -20,41 +24,44 @@ def push_head(self, value): new_node.next = self.head self.head.previous = new_node self.head = new_node - + return new_node def pop_tail(self): - if self.tail is None: raise IndexError("pop_tail from empty linked list") - + value = self.tail.value - - if self.head == self.tail: - self.head = None - self.tail = None - else: - self.tail = self.tail.previous - self.tail.next = None - + self.remove(self.tail) # Delegate actual removal to remove() return value - def remove(self, node): + def remove(self, node: Node): if node is None: raise ValueError("Cannot remove None node") - + if node == self.head == self.tail: self.head = None self.tail = None elif node == self.head: self.head = node.next - self.head.previous = None + if self.head: + self.head.previous = None elif node == self.tail: self.tail = node.previous - self.tail.next = None + if self.tail: + self.tail.next = None else: node.previous.next = node.next node.next.previous = node.previous - + node.next = None - node.previous = None \ No newline at end of file + node.previous = None + + def __iter__(self) -> Iterator: + current = self.head + while current: + yield current.value + current = current.next + + def __repr__(self) -> str: + return f"LinkedList([{', '.join(str(v) for v in self)}])" \ No newline at end of file From 8d6258cef308811d32fe73e32b780a089c65147a Mon Sep 17 00:00:00 2001 From: RahwaZeslusHaile Date: Mon, 2 Mar 2026 21:40:50 +0000 Subject: [PATCH 4/4] clearing the file --- Sprint-2/implement_linked_list/linked_list.py | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/Sprint-2/implement_linked_list/linked_list.py b/Sprint-2/implement_linked_list/linked_list.py index b5f94d7..e15fff6 100644 --- a/Sprint-2/implement_linked_list/linked_list.py +++ b/Sprint-2/implement_linked_list/linked_list.py @@ -32,7 +32,7 @@ def pop_tail(self): raise IndexError("pop_tail from empty linked list") value = self.tail.value - self.remove(self.tail) # Delegate actual removal to remove() + self.remove(self.tail) return value def remove(self, node: Node):