Day 25

day25/day25.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+
+import sys
+from collections import defaultdict
+
+from utils import io
+from utils.graph import bfs, create_dotfile
+
+
+def part1(filename, example=False):
+    graph = defaultdict(set)
+    for line in io.get_lines(filename):
+        node, neighours = line.split(": ")
+        for n in neighours.split(" "):
+            graph[node].add(n)
+            graph[n].add(node)
+
+    # visualize with neato: neato -Tpng graph.dot > graph.png; open graph.png
+    create_dotfile(graph)
+
+    # look at ^, these are
+    if example:
+        pairs = [
+            ("hfx", "pzl"),
+            ("cmg", "bvb"),
+            ("jqt", "nvd"),
+        ]
+    else:
+        pairs = [
+            ("gzr", "qnz"),
+            ("hgk", "pgz"),
+            ("xgs", "lmj"),
+        ]
+
+    for p1, p2 in pairs:
+        graph[p1].remove(p2)
+        graph[p2].remove(p1)
+
+    p = 1
+    candidates = set(graph.keys())
+    while candidates:
+        visited = bfs(candidates.pop(), graph)
+        p *= len(visited)
+        candidates -= visited
+
+    return p
+
+
+def main():
+    assert part1("example.txt", True) == 54
+    print(part1("../input/2023/day25.txt"))
+
+
+if __name__ == "__main__":
+    sys.exit(main())

day25/example.txt

@@ -0,0 +1,13 @@
+jqt: rhn xhk nvd
+rsh: frs pzl lsr
+xhk: hfx
+cmg: qnr nvd lhk bvb
+rhn: xhk bvb hfx
+bvb: xhk hfx
+pzl: lsr hfx nvd
+qnr: nvd
+ntq: jqt hfx bvb xhk
+nvd: lhk
+lsr: lhk
+rzs: qnr cmg lsr rsh
+frs: qnr lhk lsr

utils/graph.py

@@ -127,3 +127,12 @@ def dfs(node, visited):
         return max_length
 
     return dfs(start, set())
+
+
+def create_dotfile(graph):
+    with open("graph.dot", "w") as f:
+        f.write("digraph G {\n")
+        for node, neighours in graph.items():
+            for n in neighours:
+                f.write(f'"{node}" -> "{n}";\n')
+        f.write("}")