AdventOfCode2021/12/main.go

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()
				// in day 2, skip checks once we know we've visited a small room twice
				descend(rooms, link, path, success, canVisitSmallRoomTwice && !doubleSmallAlready(newPath))
			}(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))
}