Solution for 2023, day 25

Author: lucianoq

2023/25/Makefile

@@ -0,0 +1,11 @@
+main1:
+	go build -o main1 main1.go
+
+.PHONY: run1 clean
+
+run1: main1
+	./main1 <input
+
+clean:
+	rm -f main1
+

2023/25/graph.png

@@ -0,0 +1,87 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+)
+
+type Graph map[string]map[string]struct{}
+
+func (g Graph) Link(a, b string) {
+	if _, ok := g[a]; !ok {
+		g[a] = make(map[string]struct{})
+	}
+	g[a][b] = struct{}{}
+
+	if _, ok := g[b]; !ok {
+		g[b] = make(map[string]struct{})
+	}
+	g[b][a] = struct{}{}
+}
+
+func (g Graph) Unlink(a, b string) {
+	delete(g[a], b)
+	delete(g[b], a)
+}
+
+func (g Graph) Dot() string {
+	sb := strings.Builder{}
+	sb.WriteString("graph G {\n")
+	for a := range g {
+		for b := range g[a] {
+			sb.WriteString(fmt.Sprintf("\t%s -- %s\n", a, b))
+		}
+	}
+	sb.WriteString("}\n")
+	return sb.String()
+}
+
+func parse() Graph {
+	g := Graph{}
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		ff := strings.Split(line, ":")
+		left := ff[0]
+		right := strings.Fields(ff[1])
+
+		for _, r := range right {
+			g.Link(left, r)
+		}
+	}
+	return g
+}
+
+func main() {
+	g := parse()
+
+	// Uncomment the following line to print the .dot file.
+	//fmt.Println(g.Dot())
+	// Use `neato -T png graph.dot >graph.png`
+	// to generate the image included in the dir.
+
+	g.Unlink("vps", "pzc")
+	g.Unlink("xvk", "sgc")
+	g.Unlink("dph", "cvx")
+
+	fmt.Println(bfs(g, "vps") * bfs(g, "pzc"))
+}
+
+func bfs(g Graph, start string) int {
+	visited := map[string]struct{}{}
+	toDo := []string{start}
+	var curr string
+	for len(toDo) > 0 {
+		curr, toDo = toDo[0], toDo[1:]
+		for node := range g[curr] {
+			if _, ok := visited[node]; !ok {
+				visited[node] = struct{}{}
+				toDo = append(toDo, node)
+			}
+		}
+	}
+	return len(visited)
+}