AdventOfCode2021/20/main.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strings"
	"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 coord struct {
	x int
	y int
}

// grid SHOULD be like this:
//   x ->
// y
// |
// V

type image struct {
	background rune // what all uninitialized cells are set to; defaults to '.'
	grid       map[coord]rune
	topleft    coord
	size       int
}

func GetNeighbors(c coord) []coord {
	return []coord{
		{x: c.x - 1, y: c.y - 1},
		{x: c.x, y: c.y - 1},
		{x: c.x + 1, y: c.y - 1},

		{x: c.x - 1, y: c.y},
		{x: c.x, y: c.y},
		{x: c.x + 1, y: c.y},

		{x: c.x - 1, y: c.y + 1},
		{x: c.x, y: c.y + 1},
		{x: c.x + 1, y: c.y + 1},
	}
}

func (img *image) GetNewRune(coord coord, enhancementMap string) rune {
	index := 0
	coords := GetNeighbors(coord)
	for i := 0; i < len(coords); i++ {
		value := img.grid[coords[i]]
		if value == 0 {
			value = img.background
		}
		if value == '#' {
			index += (1 << (8 - i))
		}
	}
	return rune(enhancementMap[index])
}

func (img *image) CountBrightPixels() int {
	count := 0
	for _, v := range img.grid {
		if v == '#' {
			count++
		}
	}
	return count
}

func (img *image) Print() {
	fmt.Println(strings.Repeat(string(img.background), img.size+2))
	for y := img.topleft.y; y < img.size+img.topleft.y; y++ {
		fmt.Print(string(img.background))
		for x := img.topleft.x; x < img.size+img.topleft.x; x++ {
			fmt.Printf("%s", string(img.grid[coord{x, y}]))
		}
		fmt.Printf("%s\n", string(img.background))
	}
	fmt.Println(strings.Repeat(string(img.background), img.size+2))
}

func Enhance(img *image, m string) *image {
	next := &image{
		topleft: coord{
			x: img.topleft.x - 1,
			y: img.topleft.y - 1,
		},
		size: img.size + 2,
		grid: map[coord]rune{},
	}
	if img.background == '.' { // permute new "background" value
		next.background = rune(m[0])
	} else if img.background == '#' {
		next.background = rune(m[511])
	}
	for y := img.topleft.y - 1; y < img.size+1; y++ {
		for x := img.topleft.x - 1; x < img.size+1; x++ {
			next.grid[coord{x, y}] = img.GetNewRune(coord{x, y}, m)
		}
	}
	return next
}

func partOne() {
	scanner := makeScanner(false)

	scanner.Scan()
	enhancementString := scanner.Text()
	scanner.Scan() // eat empty line

	img := &image{
		background: '.',
		grid:       map[coord]rune{},
		topleft:    coord{0, 0},
	}

	y := 0
	for scanner.Scan() {
		line := scanner.Text()
		img.size = len(line)
		for x, c := range line {
			img.grid[coord{x, y}] = c
		}
		y++
	}

	for i := 0; i < 2; i++ {
		img = Enhance(img, enhancementString)
	}
	fmt.Println(img.CountBrightPixels())
}

func partTwo() {
	scanner := makeScanner(false)

	scanner.Scan()
	enhancementString := scanner.Text()
	scanner.Scan() // eat empty line

	img := &image{
		background: '.',
		grid:       map[coord]rune{},
		topleft:    coord{0, 0},
	}

	y := 0
	for scanner.Scan() {
		line := scanner.Text()
		img.size = len(line)
		for x, c := range line {
			img.grid[coord{x, y}] = c
		}
		y++
	}

	for i := 0; i < 50; i++ {
		img = Enhance(img, enhancementString)
	}
	fmt.Println(img.CountBrightPixels())
}