Update day 12 solution

day-12/day-12.py

@@ -5,13 +5,12 @@ from pathlib import Path
 def process_node(node, available_edges, visited):
     paths = []
     if node == "end":
-        return [[node]]
+        paths.append([node])
+        return paths
     if node.islower():
         visited.add(node)
-    neighbors = [[n for n in e if n != node]
-                 for e in available_edges if node in e]
+    neighbors = [n for e in available_edges if node in e for n in e if n != node]
     for n in neighbors:
-        n = n[0]
         if n not in visited:
             next = process_node(n, available_edges, visited)
             for p in next:
@@ -24,7 +23,8 @@ def process_node(node, available_edges, visited):
 def process_node_twice(node, available_edges, visited, twice):
     paths = []
     if node == "end":
-        return [[node]]
+        paths.append([node])
+        return paths
     if node.islower():
         if node in visited and twice:
             return paths
@@ -32,16 +32,14 @@ def process_node_twice(node, available_edges, visited, twice):
             twice = node
         else:
             visited.add(node)
-    neighbors = [[n for n in e if n != node]
-                 for e in available_edges if node in e]
+    neighbors = [n for e in available_edges if node in e for n in e if n != node]
     for n in neighbors:
-        n = n[0]
         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 = ""
+        twice = None
     elif node in visited:
         visited.remove(node)
     return paths
@@ -66,7 +64,7 @@ def part_2(input):
         n_start, n_end = line.strip().split('-')
         e = (n_start, n_end)
         edges.append(e)
-    paths = process_node_twice("start", edges, set(), "")
+    paths = process_node_twice("start", edges, set(), None)
     result = len(paths)
     print("Part 2 result:", result)