advent-of-code-go/2021/day13/main.go

package main

import (
	_ "embed"
	"flag"
	"fmt"
	"regexp"
	"strings"

	"github.com/alexchao26/advent-of-code-go/cast"
	"github.com/alexchao26/advent-of-code-go/halp"
	"github.com/alexchao26/advent-of-code-go/util"
)

//go:embed input.txt
var input string

func init() {
	// do this in init (not main) so test file has same input
	input = strings.TrimRight(input, "\n")
	if len(input) == 0 {
		panic("empty input.txt file")
	}
}

func main() {
	var part int
	flag.IntVar(&part, "part", 1, "part 1 or 2")
	flag.Parse()
	fmt.Println("Running part", part)

	ans := transparentOrigamiDay13(input, part)
	util.CopyToClipboard(fmt.Sprintf("%v", ans))
	fmt.Println("Output:", ans)
}

func transparentOrigamiDay13(input string, part int) int {
	parts := strings.Split(input, "\n\n")

	coords := map[[2]int]bool{}
	// parse coords
	for _, line := range strings.Split(parts[0], "\n") {
		sp := strings.Split(line, ",")
		coords[[2]int{cast.ToInt(sp[0]), cast.ToInt(sp[1])}] = true
	}

	for _, fold := range strings.Split(parts[1], "\n") {
		cap := regexp.MustCompile(`fold along (x|y)=(\d+)`).FindStringSubmatch(fold)
		// remove full match
		cap = cap[1:]

		dir := cap[0]
		foldCoord := cast.ToInt(cap[1])

		// dots will never appear exactly on a fold line
		isFoldOnX := dir == "x"
		nextMap := map[[2]int]bool{}
		if isFoldOnX {
			for c := range coords {
				if c[0] > foldCoord {
					folded := [2]int{
						foldCoord - (c[0] - foldCoord),
						c[1],
					}
					nextMap[folded] = true
				} else {
					nextMap[c] = true
				}
			}
		} else {
			// fold on y
			for c := range coords {
				if c[1] > foldCoord {
					folded := [2]int{
						c[0],
						foldCoord - (c[1] - foldCoord),
					}
					nextMap[folded] = true
				} else {
					nextMap[c] = true
				}
			}
		}

		coords = nextMap

		// return after one fold for part 1?
		if part == 1 {
			return len(coords)
		}
	}

	// printing is a pita but necessary for reading part2
	if part == 2 {
		// NOTE: as usual my printing is rotated and mirrored because my mental
		// mapping of x/y uses rows/cols and ends up different than AOC :/
		// Maybe next year I'll finally change my mental map... or not :)
		halp.PrintInfiniteGridBools(coords, "#", ".")
	}

	return 0
}