Add 2026.05.08 pre-existing code

notes-and-examples/2026.05.06/registration.py

@@ -0,0 +1,45 @@
+# from 2026.02.28
+class Node:
+    next_node: "None | Node" = None
+    prev_node: "None | Node" = None
+
+    def __init__(self, value):
+        self.value = value
+
+class Queue:
+    front: "Node | None" = None
+    back: "Node | None" = None
+
+    def append(self, value):
+        if self.back is None:
+            self.front = Node(value)
+            self.back = self.front
+        else:
+            new_node = Node(value)
+            self.back.prev_node = new_node
+            new_node.next_node = self.back
+            self.back = new_node
+    
+    def popleft(self):
+        if self.front is not None:
+            prev_front = self.front
+
+            prev_node_in_queue = self.front.prev_node
+            self.front.next_node = None
+            self.front.prev_node = None
+            if prev_node_in_queue is not None:
+                prev_node_in_queue.next_node = None
+
+            self.front = prev_node_in_queue
+            
+            return prev_front
+        else:
+            return None
+
+    def print_queue(self):
+        current_node = self.front
+        while current_node is not None:
+            print(current_node.value)
+            current_node = current_node.prev_node
+
+# from today