adventofcode/2024/day19/main.go

package main

import (
	"fmt"
	"strings"

	h "git.bullercodeworks.com/brian/adventofcode/helpers"
)

var cache map[string]int

func main() {
	inp := h.StdinToStringSlice()
	cache = make(map[string]int)
	part1(inp)
	fmt.Println()
	part2(inp)
}

func part1(inp []string) {
	available, want := parseTowels(inp)
	fmt.Println("# Part 1")
	var possible int
	for i := range want {
		if build(want[i], available) > 0 {
			possible++
		}
	}
	fmt.Println("Possible Designs:", possible)
}

func part2(inp []string) {
	available, want := parseTowels(inp)
	fmt.Println("# Part 2")
	var possible int
	for i := range want {
		possible += build(want[i], available)
	}
	fmt.Println("Possible Designs:", possible)
}

func build(towel string, from []string) int {
	if _, ok := cache[towel]; !ok {
		if len(towel) == 0 {
			return 1
		}
		res := 0
		for _, p := range from {
			if strings.HasPrefix(towel, p) {
				res += build(towel[len(p):], from)
			}
		}
		cache[towel] = res
	}
	return cache[towel]
}

/* Slow solution...
func build(towel string, from []string) bool {
	if len(towel) == 0 {
		return true
	}

	for i := range from {
		if len(from[i]) > len(towel) {
			continue
		}
		var nextFrom bool
		for j := 0; j < len(from[i]); j++ {
			if towel[j] != from[i][j] {
				nextFrom = true
				break
			}
		}
		// This 'from' didn't match
		if nextFrom {
			continue
		}
		if build(towel[len(from[i]):], from) {
			return true
		}
	}
	return false
}
*/

func parseTowels(inp []string) ([]string, []string) {
	var available, want []string
	pts := strings.Split(inp[0], ", ")
	for i := range pts {
		p := strings.TrimSpace(pts[i])
		available = append(available, p)
	}
	for _, n := range inp[2:] {
		want = append(want, n)
	}
	return available, want
}