2021-advent-13.go

package main

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

type dot struct {
	x, y int
}

type fold struct {
	lineNumer int
	direction string
}

const FOLD_PREFIX = "fold along "

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

	folds := make([]fold, 0, 8)
	dots := make([]dot, 0, 32)
	readingFolds := false
	for _, line := range strings.Split(string(bytes), "\n") {
		if strings.TrimSpace(line) == "" {
			readingFolds = true
			continue
		}
		if readingFolds {
			trimmed := strings.TrimPrefix(line, FOLD_PREFIX)
			tmp := strings.Split(trimmed, "=")
			fold := fold{}
			fold.direction = tmp[0]

			lineNumber, err := strconv.Atoi(tmp[1])
			if err != nil {
				log.Fatal(err)
			}
			fold.lineNumer = lineNumber
			folds = append(folds, fold)
		} else {
			tmp := strings.Split(line, ",")

			x, err := strconv.Atoi(tmp[0])
			if err != nil {
				log.Fatal(err)
			}
			y, err := strconv.Atoi(tmp[1])
			if err != nil {
				log.Fatal(err)
			}
			dots = append(dots, dot{x, y})

		}

	}
	return folds, dots
}

func foldPaper(paper map[dot]bool, instruction fold) {
	if instruction.direction == "x" {
		for currDot := range paper {
			if currDot.x > instruction.lineNumer {
				dx := currDot.x - instruction.lineNumer
				newX := instruction.lineNumer - dx
				delete(paper, currDot)
				newDot := dot{newX, currDot.y}
				paper[newDot] = true
			}
		}
	}
	if instruction.direction == "y" {
		for currDot := range paper {
			if currDot.y > instruction.lineNumer {
				dy := currDot.y - instruction.lineNumer
				newY := instruction.lineNumer - dy
				delete(paper, currDot)
				newDot := dot{currDot.x, newY}
				paper[newDot] = true
			}
		}
	}
}

func printPaper(paper map[dot]bool) {
	fmt.Println()
	maxX := -1
	maxY := -1
	for d := range paper {
		if d.x > maxX {
			maxX = d.x
		}
		if d.y > maxY {
			maxY = d.y
		}
	}

	for y := 0; y <= maxY; y++ {
		for x := 0; x <= maxX; x++ {
			ok := paper[dot{x, y}]
			if !ok {
				fmt.Print("  ")
			} else {
				fmt.Print("()")
			}
		}
		fmt.Println()
	}

	fmt.Println()

}

func task1(input string) {
	folds, dots := readInput(input)
	// fmt.Printf("%v %v\n", folds, dots)

	paper := make(map[dot]bool)
	for _, v := range dots {
		paper[v] = true
	}

	for _, fold := range folds {
		foldPaper(paper, fold)
	}
	// printPaper(paper)

	fmt.Printf("Day13 task1 %s - %v\n", input, len(paper))
}

func task2(input string) {
	folds, dots := readInput(input)
	// fmt.Printf("%v %v\n", folds, dots)

	paper := make(map[dot]bool)
	for _, v := range dots {
		paper[v] = true
	}

	// printPaper(paper)
	for _, fold := range folds {
		foldPaper(paper, fold)
	}

	fmt.Printf("Day13 task2 %s -\n", input)
	printPaper(paper)
}

func main() {
	task1("example.txt")
	task1("input-task1.txt")
	task2("input-task2.txt")

}