circus

y2021/p12.py

+from collections import defaultdict, Counter
+
+
+def solve(graph, part2=False):
+    edge = [('start',)]
+    final = []
+    while edge:
+        edge = [
+            route + (new,)
+            for route in edge
+            for new in graph[route[-1]]
+            if new.isupper() or route.count(new) == 0
+            or part2 & (
+                new != 'start'
+                and route.count(new) == 1
+                and max(Counter(filter(str.islower, route)).values()) == 1
+            )
+        ]
+        final.extend(el for el in edge if el[-1] == 'end')
+        edge = [el for el in edge if el[-1] != 'end']
+    return len(final)
+
+
+graph = defaultdict(set)
+for ln in text.splitlines():
+    a, b = ln.split('-')
+    graph[a].add(b)
+    graph[b].add(a)
+graph = dict(graph)
+ans1 = solve(graph)
+ans2 = solve(graph, True)