From 23d31f945eaafa8caba8ead9d4e7351cbad3f1ff Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bal=C3=A1zs=20Zaicsek?= <zebalu@gmail.com>
Date: Mon, 25 Dec 2023 07:46:09 +0100
Subject: [PATCH] Day25 -- sloow ~10 minutes

---
 .../io/github/zebalu/aoc2023/days/Day25.java  | 113 ++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 aoc2023/src/main/java/io/github/zebalu/aoc2023/days/Day25.java

diff --git a/aoc2023/src/main/java/io/github/zebalu/aoc2023/days/Day25.java b/aoc2023/src/main/java/io/github/zebalu/aoc2023/days/Day25.java
new file mode 100644
index 0000000..f686500
--- /dev/null
+++ b/aoc2023/src/main/java/io/github/zebalu/aoc2023/days/Day25.java
@@ -0,0 +1,113 @@
+package io.github.zebalu.aoc2023.days;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Queue;
+import java.util.Set;
+
+public class Day25 {
+    public static void main(String[] args) {
+        String input = readInput();
+        Map<String, Set<String>> graph = new HashMap<>();
+        input.lines().forEach(l->processLine(l, graph));
+        Map<Set<String>, Integer> edgeFrequency = new HashMap<Set<String>, Integer>();
+        List<String> vertexes = new ArrayList<>(graph.keySet());
+        for(int i=0; i<vertexes.size(); ++i) {
+            String start = vertexes.get(i);
+            for(int j=i+1; j<vertexes.size(); ++j) {
+                String target = vertexes.get(j);
+                markEdges(start, target, graph, edgeFrequency);
+            }
+        }
+        edgeFrequency.entrySet().stream().sorted(Comparator.<Entry<Set<String>, Integer>>comparingInt(e->e.getValue()).reversed()).limit(3).forEach(e->{
+            cutEdge(graph, e.getKey());
+        });
+        int part1Size = findConnectedSize(graph.keySet().iterator().next(), graph);
+        int part2Size = graph.size()-part1Size;
+        System.out.println(part1Size*part2Size);
+        System.out.println("Marry Christmas!");
+    }
+    
+    private static void markEdges(String start, String target, Map<String, Set<String>> graph,
+            Map<Set<String>, Integer> edgeFrequency) {
+        Queue<Step> queue = new LinkedList<>();
+        Set<String> visited = new HashSet<>();
+        queue.add(new Step(start, List.of()));
+        visited.add(start);
+        while (!queue.isEmpty()) {
+            Step curr = queue.poll();
+            if(target.equals(curr.vertex)) {
+                curr.edges.forEach(e->{
+                    int v = edgeFrequency.getOrDefault(e, 0);
+                    edgeFrequency.put(e, v+1);
+                });
+                return;
+            }
+            graph.get(curr.vertex).stream().filter(n->!visited.contains(n)).forEach(n->{
+                List<Set<String>> nextEdges = new ArrayList<>(curr.edges());
+                nextEdges.add(new HashSet<>(Set.of(curr.vertex, n)));
+                Step nextStep = new Step(n, nextEdges);
+                queue.add(nextStep);
+                visited.add(n);
+            });
+        }
+    }
+    
+    private static void cutEdge(Map<String, Set<String>> graph, Set<String> edge) {
+        var it = edge.iterator();
+        String a = it.next();
+        String b = it.next();
+        graph.get(a).remove(b);
+        graph.get(b).remove(a);
+    }
+    
+    private static int findConnectedSize(String start, Map<String, Set<String>> graph) {
+        Queue<String> queue = new LinkedList<>();
+        Set<String> visited = new HashSet<>();
+        queue.add(start);
+        visited.add(start);
+        while (!queue.isEmpty()) {
+            String curr = queue.poll();
+            graph.get(curr).stream().filter(n->!visited.contains(n)).forEach(n->{
+                queue.add(n);
+                visited.add(n);
+            });
+        }
+        return visited.size();
+    }
+    
+    record Step(String vertex, List<Set<String>> edges) {
+        
+    }
+
+    private static String readInput() {
+        try {
+            return Files.readString(Path.of("day25.txt").toAbsolutePath());
+        } catch (IOException e) {
+            throw new IllegalStateException(e);
+        }
+    }
+    
+    private static void processLine(String line, Map<String, Set<String>> graph) {
+        var parts = line.split(": ");
+        var name = parts[0];
+        var cons = parts[1].split(" ");
+        for(var con: cons) {
+            markConnectionn(graph, name, con);
+        }
+    }
+    
+    private static void markConnectionn(Map<String, Set<String>> graph, String from, String to) {
+        graph.computeIfAbsent(from, (k)->new HashSet<>()).add(to);
+        graph.computeIfAbsent(to, (k)->new HashSet<>()).add(from);
+    }
+}