From 679d4788d4e16c3fca7f0af9975518b5d1450848 Mon Sep 17 00:00:00 2001
From: setop <setop@zoocoop.com>
Date: Thu, 26 Dec 2024 00:35:38 +0100
Subject: [PATCH] day 23, bron kerbosch is more efficient than me

---
 d23/part2_bron_kerbosch.py | 23 +++++++++++++++++++++++
 d23/part2_naive.py         |  1 -
 2 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 d23/part2_bron_kerbosch.py

diff --git a/d23/part2_bron_kerbosch.py b/d23/part2_bron_kerbosch.py
new file mode 100644
index 0000000..4567de6
--- /dev/null
+++ b/d23/part2_bron_kerbosch.py
@@ -0,0 +1,23 @@
+from collections import defaultdict as DD
+import sys
+
+G = DD(set)
+
+for line in sys.stdin.read().strip().split('\n'):
+    a, b = line.split('-')
+    G[a].add(b)
+    G[b].add(a)
+
+def bron_kerbosch(r, p, x):
+    if len(p) == 0 and len(x) == 0:
+        yield r
+    else:
+        pivot = max(p | x, key=lambda x: len(G[x]))
+        for v in p - G[pivot]:
+            neighbours = G[v]
+            yield from bron_kerbosch(r | {v}, p & neighbours, x & neighbours)
+            p.remove(v)
+            x.add(v)
+
+clique = max(bron_kerbosch(set(), set(G.keys()), set()), key=len)
+print(','.join(sorted(clique)))
diff --git a/d23/part2_naive.py b/d23/part2_naive.py
index 6d7ad38..741d984 100644
--- a/d23/part2_naive.py
+++ b/d23/part2_naive.py
@@ -1,7 +1,6 @@
 import sys
 from collections import defaultdict as DD
 
-
 D = DD(set)
 S = set()
 for i in sys.stdin.read().strip().split('\n'):