aoc2021/thirteen/manual.go

package thirteen

import (
	"bufio"
	"fmt"
	"os"
)

type axis rune

const (
	x axis = 'x'
	y axis = 'y'
)

type fold struct {
	axis  axis
	index int
}

type manual struct {
	dots  map[int]map[int]bool
	folds []fold
}

func (m *manual) load(filename string) error {
	file, err := os.Open(filename)
	if err != nil {
		return err
	}
	defer file.Close()
	scanner := bufio.NewScanner(file)

	m.dots = map[int]map[int]bool{}
	m.folds = []fold{}
	scanningDots := true
	for scanner.Scan() {
		if scanner.Text() == "" {
			scanningDots = false
			continue
		}

		if scanningDots {
			var dotX, dotY int
			if count, err := fmt.Sscanf(scanner.Text(), "%d,%d", &dotX, &dotY); count != 2 || err != nil {
				return fmt.Errorf("expected 2 values, found %d: %w", count, err)
			}

			if m.dots[dotX] == nil {
				m.dots[dotX] = map[int]bool{}
			}

			m.dots[dotX][dotY] = true
		} else {
			var foldAxis axis
			var foldIndex int

			if count, err := fmt.Sscanf(scanner.Text(), "fold along %c=%d", &foldAxis, &foldIndex); count != 2 || err != nil {
				return fmt.Errorf("scanning %q, expected 2 values, found %d: %w", scanner.Text(), count, err)
			}

			m.folds = append(m.folds, fold{
				axis:  foldAxis,
				index: foldIndex,
			})
		}
	}
	return nil
}

func gridSize(grid map[int]map[int]bool) (xSize, ySize int) {
	for x, col := range grid {
		if x > xSize {
			xSize = x
		}
		for y := range col {
			if y > ySize {
				ySize = y
			}
		}
	}

	// // Increment Size to reflect 0 indexed arrays
	xSize++
	ySize++

	return xSize, ySize
}

func countDots(grid map[int]map[int]bool) int {
	dots := 0
	for _, col := range grid {
		for _, v := range col {
			if v {
				dots++
			}
		}
	}

	return dots
}

func (m *manual) fold() {
	grid := m.dots

	for _, inst := range m.folds {
		grid, _ = foldGrid(inst, grid)
	}

	printGrid(grid)
}

func foldGrid(inst fold, grid map[int]map[int]bool) (map[int]map[int]bool, int) {
	newGrid := map[int]map[int]bool{}

	maxX, maxY := gridSize(grid)
	if inst.axis == x {
		// Copy the first rows
		for copyX := 0; copyX < inst.index; copyX++ {
			if newGrid[copyX] == nil {
				newGrid[copyX] = map[int]bool{}
			}

			for copyY := 0; copyY < maxY; copyY++ {
				newGrid[copyX][copyY] = grid[copyX][copyY]
			}
		}

		// Copy the folded values
		for foldX := inst.index + 1; foldX < maxX; foldX++ {
			targetX := inst.index - (foldX - inst.index)
			for targetY := 0; targetY < maxY; targetY++ {
				if grid[foldX][targetY] {
					newGrid[targetX][targetY] = grid[foldX][targetY]
				}
			}
		}
	} else {
		// initialize all X maps
		for k := range grid {
			newGrid[k] = map[int]bool{}
		}

		// Copy the first rows
		for copyY := 0; copyY < inst.index; copyY++ {
			for copyX := 0; copyX < maxX; copyX++ {
				if newGrid[copyX] == nil {
					newGrid[copyX] = map[int]bool{}
				}

				newGrid[copyX][copyY] = grid[copyX][copyY]
			}
		}

		// Copy the folded values
		for foldY := inst.index + 1; foldY < maxY; foldY++ {
			targetY := inst.index - (foldY - inst.index)
			for targetX := 0; targetX < maxX; targetX++ {
				if grid[targetX][foldY] {
					newGrid[targetX][targetY] = grid[targetX][foldY]
				}
			}
		}
	}

	return newGrid, countDots(newGrid)
}

func printGrid(grid map[int]map[int]bool) {
	maxX, maxY := gridSize(grid)

	for y := 0; y < maxY; y++ {
		row := ""
		for x := 0; x < maxX; x++ {
			if grid[x][y] {
				row += "#"
			} else {
				row += " "
			}
		}
		fmt.Println(row)
	}
}