task: Day 23: LAN Party

Author: Norbiros

day_23/main.go

@@ -0,0 +1,119 @@
+package main
+
+import (
+	_ "embed"
+	"fmt"
+	"sort"
+	"strings"
+)
+
+//go:embed input.txt
+var input string
+
+func main() {
+	inputLines := strings.Split(input, "\n")
+
+	graph := make(map[string][]string)
+	for _, line := range inputLines {
+		if line == "" {
+			continue
+		}
+		elements := strings.Split(line, "-")
+		graph[elements[0]] = append(graph[elements[0]], elements[1])
+		graph[elements[1]] = append(graph[elements[1]], elements[0])
+	}
+
+	fmt.Println("Solving \"Day 23: LAN Party\"...")
+	fmt.Println("Part 1 result:", partOne(graph))
+	fmt.Println("Part 2 result:", partTwo(graph))
+}
+
+func partOne(graph map[string][]string) int {
+	count := 0
+
+	nodes := make([]string, 0, len(graph))
+	for node := range graph {
+		nodes = append(nodes, node)
+	}
+
+	for i := 0; i < len(nodes); i++ {
+		a := nodes[i]
+		for j := i + 1; j < len(nodes); j++ {
+			b := nodes[j]
+			for k := j + 1; k < len(nodes); k++ {
+				c := nodes[k]
+				if isConnected(graph, a, b) && isConnected(graph, a, c) && isConnected(graph, b, c) {
+					if strings.HasPrefix(a, "t") || strings.HasPrefix(b, "t") || strings.HasPrefix(c, "t") {
+						count++
+					}
+				}
+			}
+		}
+	}
+
+	return count
+}
+
+func partTwo(graph map[string][]string) string {
+	var maxClique []string
+
+	nodes := make([]string, 0, len(graph))
+	for node := range graph {
+		nodes = append(nodes, node)
+	}
+
+	bronKerbosch([]string{}, nodes, []string{}, graph, &maxClique)
+
+	sort.Strings(maxClique)
+	password := strings.Join(maxClique, ",")
+
+	return password
+}
+
+func bronKerbosch(r, p, x []string, graph map[string][]string, maxClique *[]string) {
+	if len(p) == 0 && len(x) == 0 {
+		if len(r) > len(*maxClique) {
+			*maxClique = append([]string{}, r...)
+		}
+		return
+	}
+
+	for i := 0; i < len(p); i++ {
+		v := p[i]
+		bronKerbosch(
+			append(r, v),
+			intersect(p, graph[v]),
+			intersect(x, graph[v]),
+			graph,
+			maxClique,
+		)
+		p = append(p[:i], p[i+1:]...)
+		x = append(x, v)
+		i--
+	}
+}
+
+func isConnected(graph map[string][]string, node1, node2 string) bool {
+	for _, neighbor := range graph[node1] {
+		if neighbor == node2 {
+			return true
+		}
+	}
+	return false
+}
+
+func intersect(a, b []string) []string {
+	set := make(map[string]bool)
+	for _, v := range b {
+		set[v] = true
+	}
+
+	var result []string
+	for _, v := range a {
+		if set[v] {
+			result = append(result, v)
+		}
+	}
+
+	return result
+}