Add linked list solution

shared/notes-and-examples/2026.02.28/linked_list_solution.py

@@ -0,0 +1,71 @@
+# Solution to 2026.01.28 homework
+
+class Node:
+    prev_node: "Node | None" = None
+    next_node: "Node | None" = None
+
+    def __init__(self, value) -> None:
+        self.value = value
+
+class LinkedList:
+    head: "Node | None" = None
+    tail: "Node | None" = None
+
+    def append(self, thing):
+        if self.head==None:
+            self.head=Node(value=thing)
+            self.tail=self.head
+            return
+
+        if self.tail is not None:
+            self.tail.next_node=Node(value=thing)
+            if self.tail.next_node is not None:
+                self.tail.next_node.prev_node = self.tail
+            self.tail=self.tail.next_node
+
+    def prepend(self, thing):
+        previous_head = self.head
+        self.head = Node(value=thing)
+        self.head.next_node = previous_head
+
+        if previous_head is not None:
+            previous_head.prev_node = self.head
+
+    def insert(self, thing, index):
+        current_node = self.head
+        if current_node is None:
+            self.append(thing)
+            return
+
+        if index == 0:
+            self.prepend(thing)
+            return
+        
+        for _ in range(1, index):
+            if current_node is not None:
+                current_node = current_node.next_node
+        if current_node is None:
+            raise IndexError 
+
+        prev_next = current_node.next_node
+        current_node.next_node = Node(thing)
+        current_node.next_node.prev_node = current_node 
+        current_node.next_node.next_node = prev_next
+
+    
+    def print_list(self):
+        current_node = self.head
+        while current_node is not None:
+            print(current_node.value)
+            current_node = current_node.next_node
+
+example_list = LinkedList()
+example_list.append("first")
+example_list.append("second")
+example_list.append("fourth")
+example_list.insert("third", 2)
+example_list.insert("zero", 0)
+example_list.insert("last", 5)
+
+example_list.print_list()
+