Update day 12 solution

Speed up a little and rename argument twice to visited_twice

day-12/day-12.py

@@ -12,34 +12,32 @@ def process_node(node, available_edges, visited):
     neighbors = [n for e in available_edges if node in e for n in e if n != node]
     for n in neighbors:
         if n not in visited:
-            next = process_node(n, available_edges, visited)
-            for p in next:
-                paths.append([node] + p)
+            nxt = process_node(n, available_edges, visited)
+            paths = [[node] + p for p in nxt]
     if node in visited:
         visited.remove(node)
     return paths
 
 
-def process_node_twice(node, available_edges, visited, twice):
+def process_node_twice(node, available_edges, visited, visited_twice):
     paths = []
     if node == "end":
         paths.append([node])
         return paths
     if node.islower():
-        if node in visited and twice:
+        if node in visited and visited_twice:
             return paths
         elif node in visited and node != "start":
-            twice = node
+            visited_twice = node
         else:
             visited.add(node)
     neighbors = [n for e in available_edges if node in e for n in e if n != node]
     for n in neighbors:
-        if n not in visited or twice != node and n != "start":
-            next = process_node_twice(n, available_edges, visited, twice)
-            for p in next:
-                paths.append([node] + p)
-    if twice == node:
-        twice = None
+        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]
+    if visited_twice == node:
+        visited_twice = None
     elif node in visited:
         visited.remove(node)
     return paths