2021-advent-12.go

package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"strings"
)

func readInput(input string) map[string][]string {
	bytes, err := ioutil.ReadFile(input)
	if err != nil {
		log.Fatal(err)
	}

	ret := make(map[string][]string)
	for _, line := range strings.Split(string(bytes), "\n") {
		x := strings.Split(line, "-")

		c1 := x[0]
		c2 := x[1]

		add := func(from string, to string) {
			// fmt.Printf("%s-%s\n", from, to)
			if from != "end" && to != "start" {
				val, ok := ret[from]
				if !ok {
					ret[from] = make([]string, 0)
				}
				val = append(val, to)
				ret[from] = val
			}
		}
		add(c1, c2)
		add(c2, c1)

	}
	return ret
}

func visitOnlyOnceIfLowercase(item string, path []string) bool {
	if strings.ToLower(item) == item && contains(item, path) {
		return false
	}
	return true
}

func lowerCaseMaxTwice(item string, path []string) bool {
	counts := make(map[string]int)
	wasTwice := false
	for _, v := range path {
		if strings.ToLower(v) == v {
			counts[v]++
			if counts[v] == 2 {
				wasTwice = true
			}
		}
	}
	if wasTwice {
		return counts[item] == 0
	} else {
		return counts[item] < 2
	}
}

func step(paths map[string][]string, node string, path []string,
	validMove func(string, []string) bool) int {
	count := 0
	moves := paths[node]
	for _, v := range moves {
		//check if valid move
		if !validMove(v, path) {
			continue
		}
		if v == "end" {
			wholePath := make([]string, len(path))
			copy(wholePath, path)
			wholePath = append(wholePath, v)
			count += 1
		} else {
			pathHere := make([]string, len(path))
			copy(pathHere, path)
			pathHere = append(pathHere, v)
			count += step(paths, v, pathHere, validMove)
		}
	}
	return count
}

func contains(s string, list []string) bool {
	for _, v := range list {
		if v == s {
			return true
		}
	}
	return false
}

func task1(input string) {
	paths := readInput(input)
	numberOfPaths := step(paths, "start", []string{"start"}, visitOnlyOnceIfLowercase)
	fmt.Printf("Day12 task1 %s - %d\n", input, numberOfPaths)

}

func task2(input string) {
	paths := readInput(input)
	numberOfPaths := step(paths, "start", []string{"start"}, lowerCaseMaxTwice)
	fmt.Printf("Day12 task1 %s - %d\n", input, numberOfPaths)

}

func main() {
	// fmt.Printf("%+v", paths)
	task1("example1.txt")
	task1("example2.txt")
	task1("example3.txt")
	task1("input.txt")

	task2("example1.txt")
	task2("example2.txt")
	task2("example3.txt")
	task2("input.txt")
}