aoc21/13/main.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"strconv"
	"strings"
)

type FoldAxis bool

const (
	Y FoldAxis = false
	X FoldAxis = true
)

type Fold struct {
	direction FoldAxis
	line      int
}

func main() {
	grid, folds := setUpGrid()

	var count int
	for i, f := range folds {
		grid, count = fold(&grid, f.direction, f.line)
		if i == 0 {
			fmt.Println(count)
		}
	}

	for y := 0; y < len(grid); y++ {
		for x := 0; x < len(grid[0]); x++ {
			if grid[y][x] == 1 {
				fmt.Print("█")
			} else {
				fmt.Print(" ")
			}
		}
		fmt.Println()
	}
}

func fold(g *[][]int, axis FoldAxis, line int) (grid [][]int, count int) {
	count = 0
	if axis == Y {
		grid = make([][]int, line)
		for i := range grid {
			grid[i] = make([]int, len((*g)[0]))
		}

		for i := 1; i+line < len(*g) && line-i >= 0; i++ {
			aboveLine, belowLine := (*g)[i+line], (*g)[line-i]
			newLine := make([]int, len(aboveLine))
			for colNum := range newLine {
				if aboveLine[colNum] == 1 || belowLine[colNum] == 1 {
					newLine[colNum] = 1
					count++
				}
			}
			grid[line-i] = newLine
		}
	} else if axis == X {
		grid = make([][]int, len(*g))
		for i := range grid {
			grid[i] = make([]int, line)
		}
		for i1, v := range *g {
			for i := 0; i < line; i++ {
				if v[i] == 1 || v[len(v)-1-i] == 1 {
					grid[i1][i] = 1
					count++
				} else {
					grid[i1][i] = 0
				}
			}
		}
	}
	return
}

func setUpGrid() (grid [][]int, folds []Fold) {
	folds = make([]Fold, 0)
	file, err := os.Open("input.txt")
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)
	scanner.Split(bufio.ScanLines)

	var maxX, maxY int
	dots := make([][]int, 0)
	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			continue
		} else if strings.HasPrefix(line, "fold along x") {
			f := Fold{X, 0}
			fmt.Sscanf(line, "fold along x=%d", &f.line)
			folds = append(folds, f)
		} else if strings.HasPrefix(line, "fold along y") {
			f := Fold{Y, 0}
			fmt.Sscanf(line, "fold along y=%d", &f.line)
			folds = append(folds, f)
		} else {
			dotPoints := strings.Split(line, ",")
			dotPointsInt := make([]int, 2)
			for i, v := range dotPoints {
				num, _ := strconv.Atoi(v)
				dotPointsInt[i] = num
				if i == 0 && num > maxX {
					maxX = num
				}
				if i == 1 && num > maxY {
					maxY = num
				}
			}
			dots = append(dots, dotPointsInt)
		}
	}
	grid = make([][]int, maxY+1)
	for i := range grid {
		grid[i] = make([]int, maxX+1)
	}

	for _, v := range dots {
		grid[v[1]][v[0]] = 1
	}
	return
}