2021-advent-20.go

package main

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

// Image enhancing algorithms
type IEA []rune

type Image [][]rune

func (iea IEA) String() string {
	return string(iea)
}

func (iea Image) String() string {
	sb := strings.Builder{}
	sb.WriteString("\n")
	for _, v := range iea {
		sb.WriteString(string(v))
		sb.WriteString("\n")
	}
	return sb.String()
}

func (img Image) Lits() int {
	counter := 0
	for _, row := range img {
		for _, rune := range row {
			if rune == '#' {
				counter += 1
			}
		}
	}
	return counter
}

func readInput(file string) (IEA, Image) {
	bytes, err := ioutil.ReadFile(file)
	if err != nil {
		log.Fatal(err)
	}
	S := strings.Split(string(bytes), "\n\n")

	IEA := make(IEA, 0)
	for _, rune := range S[0] {
		IEA = append(IEA, rune)
	}

	image := make(Image, 0)
	for _, line := range strings.Split(S[1], "\n") {
		image = append(image, []rune(line))
	}
	return IEA, image
}

func tranform(in string) int {
	l := len(in) - 1
	counter := 0
	for i, v := range in {
		if v == '#' {
			counter += int(math.Pow(2, float64((l - i))))
		}
	}
	return counter
}

func task(input string, iteration int) {
	iea, image := readInput(input)

	background := '.'
	for it := 0; it < iteration; it++ {
		lenY := len(image)
		lenX := len(image[0])

		getPoint := func(x, y int, bgk rune) rune {
			if x < 0 || x >= lenX {
				return bgk
			}
			if y < 0 || y >= lenY {
				return bgk
			}
			return image[y][x]
		}

		nextImage := make(Image, lenY+2)
		for yi := -1; yi < lenY+1; yi++ {
			for xi := -1; xi < lenX+1; xi++ {
				s := ""
				for i := -1 + yi; i <= 1+yi; i++ {
					for j := -1 + xi; j <= 1+xi; j++ {
						s += string(getPoint(j, i, background))
					}
				}
				index := tranform(s)
				nextImage[yi+1] = append(nextImage[yi+1], iea[index])
			}
		}
		image = nextImage

		switch background {
		case '.':
			background = iea[tranform(".........")]
		case '#':
			background = iea[tranform("#########")]
		}

	}
	fmt.Printf("Day20 nr of iteration %d  %s - %v\n", iteration, input, image.Lits())
}

func main() {

	// 35
	task("example.txt", 2)

	// 4964
	task("input.txt", 2)

	// 3351
	task("example.txt", 50)

	// 13202
	task("input.txt", 50)
}