day12: python

Honestly, I was stunned when my part1 worked first time.

Part 2 was harder because I'm an idiot and had a bug that kept causing recursion errors.

Reckon I'll do a refactor to combine the two parts and memoise, since part 2 took rather long

day12/day12.py

@@ -0,0 +1,99 @@
+from collections import Counter, defaultdict
+
+
+def load_data(path):
+    graph = defaultdict(list)
+
+    with open(path, 'r') as f:
+        for line in f:
+
+            a, b = line.strip().split('-')
+
+            if a == 'start':
+                graph['START'].append(b)
+            elif b == 'start':
+                graph['START'].append(a)
+
+            elif b == 'end':
+                graph[a].append('END')
+            elif a == 'end':
+                graph[b].append('END')
+
+            else:
+                graph[a].append(b)
+                graph[b].append(a)
+
+    return graph
+
+
+def count_paths(graph, node, visited):
+    if node == 'END':
+        return 1
+
+    neighbours = [
+        n for n in graph[node]
+        if n.isupper() or n not in visited
+    ]
+
+    paths = 0
+    for n in neighbours:
+        paths += count_paths(graph, n, {n, *visited})
+
+    return paths
+
+
+def part1(graph):
+    return count_paths(graph, 'START', set())
+
+
+def count_paths_with_revisit(graph, node, visited):
+    if node == 'END':
+        return 1
+
+    can_revisit = not any(v == 2 for v in visited.values())
+
+    paths = 0
+    for n in graph[node]:
+        if n.isupper():
+            paths += count_paths_with_revisit(graph, n, visited)
+        elif visited[n] == 0 or can_revisit:
+            v = visited.copy()
+            v[n] += 1
+            paths += count_paths_with_revisit(graph, n, v)
+
+    return paths
+
+
+def part2(graph):
+    return count_paths_with_revisit(graph, 'START', Counter())
+
+
+def main():
+    data = load_data('input.txt')
+    print(part1(data))
+    print(part2(data))
+
+
+if __name__ == '__main__':
+    main()
+
+
+class Test:
+
+    def test_part1_small(self):
+        assert part1(load_data('test.txt')) == 10
+
+    def test_part1_medium(self):
+        assert part1(load_data('test1.txt')) == 19
+
+    def test_part1_large(self):
+        assert part1(load_data('test2.txt')) == 226
+
+    def test_part2_small(self):
+        assert part2(load_data('test.txt')) == 36
+
+    def test_part2_medium(self):
+        assert part2(load_data('test1.txt')) == 103
+
+    def test_part2_large(self):
+        assert part2(load_data('test2.txt')) == 3509

day12/input.txt

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+by-TW
+start-TW
+fw-end
+QZ-end
+JH-by
+ka-start
+ka-by
+end-JH
+QZ-cv
+vg-TI
+by-fw
+QZ-by
+JH-ka
+JH-vg
+vg-fw
+TW-cv
+QZ-vg
+ka-TW
+ka-QZ
+JH-fw
+vg-hu
+cv-start
+by-cv
+ka-cv

day12/test.txt

@@ -0,0 +1,7 @@
+start-A
+start-b
+A-c
+A-b
+b-d
+A-end
+b-end

day12/test1.txt

@@ -0,0 +1,10 @@
+dc-end
+HN-start
+start-kj
+dc-start
+dc-HN
+LN-dc
+HN-end
+kj-sa
+kj-HN
+kj-dc

day12/test2.txt

@@ -0,0 +1,18 @@
+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