Solution for 2024, day 23

Author: lucianoq

2024/23/Makefile

@@ -0,0 +1,20 @@
+input:
+	http "https://adventofcode.com/2024/day/23/input" "Cookie:session=${AOC_SESSION};" >input
+
+main1:
+	go build -o main1 main1.go common.go
+
+main2:
+	go build -o main2 main2.go common.go
+
+.PHONY: run1 run2 clean
+
+run1: main1 input
+	./main1 <input
+
+run2: main2 input
+	./main2 <input
+
+clean:
+	rm -f main1 main2 input
+

2024/23/common.go

@@ -0,0 +1,93 @@
+package main
+
+import (
+	"bufio"
+	"os"
+	"sort"
+	"strings"
+)
+
+type Set map[string]struct{}
+
+func (s *Set) ToKey(others ...string) string {
+	list := make([]string, 0, len(*s)+len(others))
+	for k := range *s {
+		list = append(list, k)
+	}
+	for _, other := range others {
+		list = append(list, other)
+	}
+	sort.Strings(list)
+	return strings.Join(list, ",")
+}
+
+func (s *Set) FromKey(key string) {
+	m := Set{}
+	for _, s := range strings.Split(key, ",") {
+		m[s] = struct{}{}
+	}
+	*s = m
+}
+
+type Graph map[string]Set
+
+func (g Graph) AddEdge(from, to string) {
+	if _, ok := g[from]; !ok {
+		g[from] = Set{}
+	}
+	g[from][to] = struct{}{}
+}
+
+func (g Graph) Connected(from, to string) bool {
+	if f, ok := g[from]; ok {
+		_, ok := f[to]
+		return ok
+	}
+	return false
+}
+
+func (g Graph) Keys() Set {
+	keys := Set{}
+	for n := range g {
+		keys[n] = struct{}{}
+	}
+	return keys
+}
+
+func parseInput() Graph {
+	graph := Graph{}
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		ff := strings.Split(scanner.Text(), "-")
+		graph.AddEdge(ff[0], ff[1])
+		graph.AddEdge(ff[1], ff[0])
+	}
+	return graph
+}
+
+func (g Graph) Expand(clusters Set) Set {
+	res := Set{}
+	for clusterStr := range clusters {
+		cluster := Set{}
+		cluster.FromKey(clusterStr)
+		for node := range g[clusterStr[:2]] {
+			if _, ok := cluster[node]; ok {
+				continue
+			}
+			if !g.connectedToAll(node, cluster) {
+				continue
+			}
+			res[cluster.ToKey(node)] = struct{}{}
+		}
+	}
+	return res
+}
+
+func (g Graph) connectedToAll(node string, cluster Set) bool {
+	for old := range cluster {
+		if !g.Connected(old, node) {
+			return false
+		}
+	}
+	return true
+}

2024/23/main1.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func main() {
+	g := parseInput()
+
+	res := g.Keys()     // single nodes
+	res = g.Expand(res) // pairs
+	res = g.Expand(res) // triplets
+
+	count := 0
+	for c := range res {
+		if c[0] == 't' || strings.Contains(c, ",t") {
+			count++
+		}
+	}
+	fmt.Println(count)
+}

2024/23/main2.go

@@ -0,0 +1,17 @@
+package main
+
+import "fmt"
+
+func main() {
+	g := parseInput()
+
+	var lastNotEmpty Set
+	for res := g.Keys(); len(res) > 0; res = g.Expand(res) {
+		lastNotEmpty = res
+	}
+
+	for k := range lastNotEmpty {
+		fmt.Println(k)
+		return
+	}
+}