Day 12 in Python

Author: mlukaszek

day12.py

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+import sys
+from collections import defaultdict
+
+class Path(object):
+    def __init__(self, nodes, canVisitTwice=True) -> None:
+        self.nodes = nodes
+        self.canVisitTwice = canVisitTwice
+
+def count_paths(connections, part2=False):
+    paths = [ Path(["start"]) ]
+    total = 0
+    
+    while paths:
+        path = paths.pop()
+        lastNode = path.nodes[-1]
+        for cave in connections[lastNode]:
+            if cave == "end":
+                total += 1
+            elif part2 and cave == "start":
+                continue                
+            elif cave not in path.nodes or cave.isupper(): # first visit, or a large cave
+                paths.append( Path(path.nodes + [cave], path.canVisitTwice) )
+            elif part2 and path.canVisitTwice: # a small cave visited twice in this path, allow no more
+                paths.append( Path(path.nodes + [cave], False) )
+    return total
+
+def main(args = ()):
+    fileName = "day12.txt" if len(args) < 1 else args[0]
+
+    connections = defaultdict(list)
+    with open(fileName) as lines:
+        for edge in lines:
+            edge = edge.strip()
+            if edge:
+                a, b = edge.split("-")
+                connections[a].append(b)
+                connections[b].append(a)
+
+    print("Part 1:", count_paths(connections))
+    print("Part 2:", count_paths(connections, True))
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv[1:]))

day12.txt

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+yw-MN
+wn-XB
+DG-dc
+MN-wn
+yw-DG
+start-dc
+start-ah
+MN-start
+fi-yw
+XB-fi
+wn-ah
+MN-ah
+MN-dc
+end-yw
+fi-end
+th-fi
+end-XB
+dc-XB
+yw-XN
+wn-yw
+dc-ah
+MN-fi
+wn-DG

day12sample1.txt

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+start-A
+start-b
+A-c
+A-b
+b-d
+A-end
+b-end

day12sample2.txt

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+dc-end
+HN-start
+start-kj
+dc-start
+dc-HN
+LN-dc
+HN-end
+kj-sa
+kj-HN
+kj-dc

day12sample3.txt

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+fs-end
+he-DX
+fs-he
+start-DX
+pj-DX
+end-zg
+zg-sl
+zg-pj
+pj-he
+RW-he
+fs-DX
+pj-RW
+zg-RW
+start-pj
+he-WI
+zg-he
+pj-fs
+start-RW