Update day 12 solution

Use deque instead of list

day-12/day-12.py

@@ -1,11 +1,12 @@
 #!/usr/bin/env python3
 from pathlib import Path
+from collections import deque
 
 
 def process_node(node, available_edges, visited):
-    paths = []
+    paths = deque()
     if node == "end":
-        paths.append([node])
+        paths.append(deque(node))
         return paths
     if node.islower():
         visited.add(node)
@@ -13,16 +14,18 @@ def process_node(node, available_edges, visited):
     for n in neighbors:
         if n not in visited:
             nxt = process_node(n, available_edges, visited)
-            paths += [[node] + p for p in nxt]
+            for p in nxt:
+                p.appendleft(node)
+                paths.append(p)
     if node in visited:
         visited.remove(node)
     return paths
 
 
 def process_node_twice(node, available_edges, visited, visited_twice):
-    paths = []
+    paths = deque()
     if node == "end":
-        paths.append([node])
+        paths.append(deque(node))
         return paths
     if node.islower():
         if node in visited and visited_twice:
@@ -35,7 +38,9 @@ def process_node_twice(node, available_edges, visited, visited_twice):
     for n in neighbors:
         if n not in visited or visited_twice != node and n != "start":
             nxt = process_node_twice(n, available_edges, visited, visited_twice)
-            paths += [[node] + p for p in nxt]
+            for p in nxt:
+                p.appendleft(node)
+                paths.append(p)
     if visited_twice == node:
         visited_twice = None
     elif node in visited: