Completed day 23 of year 2024

Author: fschatbot

2024/23.py

@@ -0,0 +1,77 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+split_data = True
+completed = True
+raw_data = None # Not To be touched
+
+def part1(data):	
+	pairings = {}
+	for line in data:
+		# print(line)
+		a, b = line.split('-')
+		if a not in pairings:
+			pairings[a] = set()
+		if b not in pairings:
+			pairings[b] = set()
+		
+		pairings[a].add(b)
+		pairings[b].add(a)
+
+	# In order to find a triangle you simply take the intersection of pair[a] and pair[b]
+	# This will give you the commons of pair a and pair b which would c. Therefore, a triangle.
+	commons = set()
+	for line in data:
+		a, b = line.split('-')
+		common = pairings[a] & pairings[b]
+		for c in common:
+			if a[0] != 't' and b[0] != 't' and c[0] != 't': continue
+			tri = tuple(sorted([a,b,c]))
+			commons.add(tri)
+	
+	return len(commons)
+
+def part2(data):
+	pairings = {}
+	for line in data:
+		# print(line)
+		a, b = line.split('-')
+		if a not in pairings:
+			pairings[a] = set()
+		if b not in pairings:
+			pairings[b] = set()
+		
+		pairings[a].add(b)
+		pairings[b].add(a)
+
+	# The below is what I implemented on my own. It works but is highly inefficient...
+	"""
+	def recurse(curr_set):
+		if len(curr_set) == 0:
+			return 0
+		
+		return max(recurse(curr_set & pairings[i]) for i in curr_set) + 1
+	
+	return recurse(set(pairings.keys()))
+	"""
+
+	# Bron-Kerbosch algorithm with pivoting...
+	def BronKerbosch2(R:set, P:set, X:set):
+		if len(P) == 0 and len(X) == 0:
+			return R
+		
+		u = list(P | X)[0]
+		max_R = set()
+		max_len = 0
+		for v in P - pairings[u]:
+			r = BronKerbosch2(R | {v}, P & pairings[v], X & pairings[v])
+			if len(r) > max_len:
+				max_len = len(r)
+				max_R = r
+			P.remove(v)
+			X.add(v)
+		
+		return max_R
+	
+	max_R = BronKerbosch2(set(), set(pairings.keys()), set())
+	return ','.join(sorted(tuple(max_R)))