From 6fe9d251bd29b7e988503bc04aab4bb74219e88a Mon Sep 17 00:00:00 2001
From: David Ashby <delta.mu.alpha@gmail.com>
Date: Sun, 12 Dec 2021 13:03:33 -0500
Subject: [PATCH] day 12

---
 12/main.go | 150 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 150 insertions(+)
 create mode 100644 12/main.go

diff --git a/12/main.go b/12/main.go
new file mode 100644
index 0000000..4fda966
--- /dev/null
+++ b/12/main.go
@@ -0,0 +1,150 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+	"sync"
+	"time"
+)
+
+func main() {
+	start := time.Now()
+	partOne()
+	duration := time.Since(start)
+	partTwo()
+	duration2 := time.Since(start)
+	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
+}
+
+func makeScanner(test bool) *bufio.Scanner {
+	var f *os.File
+	if test {
+		f, _ = os.Open("inputs/testinput")
+	} else {
+		f, _ = os.Open("inputs/input")
+	}
+	reader := bufio.NewReader(f)
+	return bufio.NewScanner(reader)
+}
+
+type room struct {
+	name  string
+	links []string
+}
+
+func isBigRoom(name string) bool {
+	return strings.ToUpper(name) == name
+}
+
+func canVisit(targetRoom room, visitedRooms []string) bool {
+	if isBigRoom(targetRoom.name) {
+		return true
+	}
+	for _, v := range visitedRooms {
+		if targetRoom.name == v {
+			return false
+		}
+	}
+	return true
+}
+
+func doubleSmallAlready(visitedRooms []string) bool {
+	counts := map[string]int{}
+	for _, v := range visitedRooms {
+		counts[v]++
+	}
+	for room, v := range counts {
+		if v == 2 && !isBigRoom(room) {
+			return true
+		}
+	}
+	return false
+}
+
+func descend(rooms map[string]room, currentRoom string, path []string, success chan bool, canVisitSmallRoomTwice bool) {
+	var wg sync.WaitGroup
+	if currentRoom == "end" {
+		success <- true
+		return
+	}
+	for _, link := range rooms[currentRoom].links {
+		newPath := []string{currentRoom}
+		newPath = append(newPath, path...)
+		if canVisit(rooms[link], path) || // part one
+			(canVisitSmallRoomTwice && !doubleSmallAlready(newPath) && link != "start") { // part two
+			wg.Add(1)
+			go func(link string, path []string) {
+				defer wg.Done()
+				descend(rooms, link, path, success, canVisitSmallRoomTwice)
+			}(link, newPath)
+		}
+	}
+	wg.Wait()
+}
+
+func partOne() {
+	scanner := makeScanner(false)
+
+	rooms := map[string]room{}
+	for scanner.Scan() {
+		line := scanner.Text()
+		p := strings.Split(line, "-")
+		// create rooms if we haven't seen them before
+		if _, ok := rooms[p[0]]; !ok {
+			rooms[p[0]] = room{name: p[0]}
+		}
+		if _, ok := rooms[p[1]]; !ok {
+			rooms[p[1]] = room{name: p[1]}
+		}
+		// set up links
+		a := rooms[p[0]]
+		b := rooms[p[1]]
+		a.links = append(a.links, rooms[p[1]].name)
+		b.links = append(b.links, rooms[p[0]].name)
+		rooms[p[0]] = a
+		rooms[p[1]] = b
+	}
+	successes := make(chan bool, 10000)
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		descend(rooms, "start", []string{}, successes, false)
+	}()
+	wg.Wait()
+	fmt.Printf("%+v\n", len(successes))
+}
+func partTwo() {
+	scanner := makeScanner(false)
+
+	rooms := map[string]room{}
+	for scanner.Scan() {
+		line := scanner.Text()
+		p := strings.Split(line, "-")
+		// create rooms if we haven't seen them before
+		if _, ok := rooms[p[0]]; !ok {
+			rooms[p[0]] = room{name: p[0]}
+		}
+		if _, ok := rooms[p[1]]; !ok {
+			rooms[p[1]] = room{name: p[1]}
+		}
+		// set up links
+		a := rooms[p[0]]
+		b := rooms[p[1]]
+		a.links = append(a.links, rooms[p[1]].name)
+		b.links = append(b.links, rooms[p[0]].name)
+		rooms[p[0]] = a
+		rooms[p[1]] = b
+	}
+	successes := make(chan bool, 200000)
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		descend(rooms, "start", []string{}, successes, true)
+	}()
+	wg.Wait()
+	fmt.Printf("%+v\n", len(successes))
+}