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day 13
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/* Day 13: Transparent Origami */
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package main
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import (
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"AoC2021/utils/log"
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"AoC2021/utils/timer"
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"bufio"
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"os"
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"strconv"
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"strings"
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)
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func check(e error) {
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if e != nil {
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log.Println(log.DEBUG, "Oh snap!")
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panic(e)
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}
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}
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func main() {
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log.Println(log.NORMAL, "--- Day 13: Transparent Origami ---")
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timer.Start()
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part1()
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timer.Tick()
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log.Println(log.NORMAL)
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part2()
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timer.Tick()
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log.Println(log.NORMAL)
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}
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func part1() {
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log.Println(log.NORMAL, "* Part 1 *")
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log.Println(log.NORMAL, " Goal: The transparent paper is pretty big, so for now, focus on just completing the first fold.")
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log.Println(log.NORMAL, " Answer: How many dots are visible after completing just the first fold instruction on your transparent paper?")
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points, folds := readInput()
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grid := initGrid(points)
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dotCount := countDots(grid)
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log.Printf(log.DEBUG, "Initialized a grid of size %d by %d with %d dots\n", len(grid[0]), len(grid), dotCount)
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grid = applyFold(grid, folds[0])
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dotCount = countDots(grid)
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log.Printf(log.NORMAL, "After the first fold, the grid is now %d by %d with %d dots\n", len(grid[0]), len(grid), dotCount)
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}
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func part2() {
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log.Println(log.NORMAL, "* Part 2 *")
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log.Println(log.NORMAL, " Goal: Finish folding the transparent paper according to the instructions. The manual says the code is always eight capital letters.")
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log.Println(log.NORMAL, " Answer: What code do you use to activate the infrared thermal imaging camera system?")
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points, folds := readInput()
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grid := initGrid(points)
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dotCount := countDots(grid)
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log.Printf(log.DEBUG, "Initialized a grid of size %d by %d with %d dots\n", len(grid[0]), len(grid), dotCount)
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for fIdx, fold := range folds {
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grid = applyFold(grid, fold)
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dotCount = countDots(grid)
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log.Printf(log.DEBUG, "After the fold #%d, the grid is now %d by %d with %d dots\n", fIdx+1, len(grid[0]), len(grid), dotCount)
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}
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log.Printf(log.NORMAL, "After %d folds the grid is %d by %d and has %d dots\n", len(folds), len(grid[0]), len(grid), dotCount)
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log.Printf(log.NORMAL, "The secret code in ASCII format is:\n")
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printGrid(grid)
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log.Printf(log.NORMAL, "(You figure it out. Your brain will work better than janky OCR\n")
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}
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type Point struct {
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x, y int
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}
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type Fold struct {
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direction string
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value int
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}
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func readInput() ([]Point, []Fold) {
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input, err := os.Open("./input.txt")
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check(err)
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defer input.Close()
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scanner := bufio.NewScanner(input)
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lines := 0
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// Read Coordinates
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var points []Point
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for scanner.Scan() {
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line := scanner.Text()
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lines++
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if line == "" {
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break
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}
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coords := strings.Split(line, ",")
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x, err := strconv.Atoi(coords[0])
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check(err)
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y, err := strconv.Atoi(coords[1])
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check(err)
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points = append(points, Point{x, y})
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}
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// Read Instructions
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const INSTRUCTION_PREFIX = "fold along "
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const INSTRUCTION_PREFIX_LEN = len(INSTRUCTION_PREFIX)
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var folds []Fold
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for scanner.Scan() {
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line := scanner.Text()
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lines++
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if strings.Contains(line, INSTRUCTION_PREFIX) {
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instruction := strings.Split(line[INSTRUCTION_PREFIX_LEN:], "=")
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direction := instruction[0]
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value, err := strconv.Atoi(instruction[1])
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check(err)
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folds = append(folds, Fold{direction, value})
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}
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}
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log.Printf(log.DEBUG, "Read %d coordinates and %d fold instructions from %d lines\n", len(points), len(folds), lines)
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return points, folds
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}
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func getMaxSize(points []Point) (int, int) {
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maxX, maxY := 0, 0
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for _, point := range points {
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if point.x > maxX {
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maxX = point.x
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}
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if point.y > maxY {
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maxY = point.y
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}
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}
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log.Printf(log.DIAGNOSTIC, "Max size is %d wide by %d tall\n", maxX, maxY)
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return maxX, maxY
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}
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type Grid = [][]bool
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func initGrid(points []Point) Grid {
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maxX, maxY := getMaxSize(points)
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grid := make(Grid, maxY+1)
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for y := 0; y <= maxY; y++ {
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grid[y] = make([]bool, maxX+1)
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}
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for _, point := range points {
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grid[point.y][point.x] = true
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}
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log.Printf(log.DIAGNOSTIC, "Marked %d points on the grid\n", len(points))
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return grid
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}
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func applyFold(grid Grid, fold Fold) Grid {
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if len(grid) == 0 {
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panic("Cannot process empty grid")
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}
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log.Printf(log.DEBUG, "Applying fold {%s=%d} to grid\n", fold.direction, fold.value)
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startY, startX, dirY, dirX := 0, 0, 1, 1
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if fold.direction == "y" {
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startY = fold.value
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dirY = -1
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}
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if fold.direction == "x" {
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startX = fold.value
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dirX = -1
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}
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ovDots := 0
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newDots := 0
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for y := startY; y < len(grid); y++ {
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for x := startX; x < len(grid[y]); x++ {
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if grid[y][x] {
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// to flip a point, we basically move it as far 'left' or 'up' from the fold point as it was 'right' or 'down'
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newX, newY := 2*startX+dirX*x, 2*startY+dirY*y
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log.Printf(log.DIAGNOSTIC, "Drawing (%d, %d) to (%d, %d)", x, y, newX, newY)
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if grid[newY][newX] {
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ovDots++
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log.Println(log.DIAGNOSTIC, " Ov")
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} else {
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newDots++
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log.Println(log.DIAGNOSTIC, " (new)")
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}
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grid[newY][newX] = true
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}
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}
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}
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log.Printf(log.DIAGNOSTIC, "Overwrite %d dots and added %d dots\n", ovDots, newDots)
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// chop the grid either width- or length-wise as appropriate
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if fold.direction == "y" {
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grid = grid[:startY]
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} else if fold.direction == "x" {
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for y, row := range grid {
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grid[y] = row[:startX]
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}
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}
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return grid
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}
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// count the number of dots in the grid
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func countDots(grid Grid) int {
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count := 0
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for _, row := range grid {
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for _, value := range row {
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if value {
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count++
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}
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}
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}
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return count
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}
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func printGrid(grid Grid) {
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log.Printf(log.NORMAL, "/%s\\\n", nTimesStr("=", len(grid[0])))
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for _, row := range grid {
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log.Print(log.NORMAL, "|")
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for _, value := range row {
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switch value {
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case false:
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log.Print(log.NORMAL, " ")
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case true:
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log.Print(log.NORMAL, "*")
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}
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}
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log.Println(log.NORMAL, "|")
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}
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log.Printf(log.NORMAL, "\\%s/\n", nTimesStr("=", len(grid[0])))
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}
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func nTimesStr(s string, t int) string {
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newStr := ""
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for c := 0; c < t; c++ {
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newStr += s
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}
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return newStr
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}
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@@ -0,0 +1,11 @@
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package main
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import (
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"AoC2021/utils/assert"
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"testing"
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)
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func TestDay13(t *testing.T) {
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assert.IsTrue(t, true, "cool")
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assert.EqualsStr(t, "foo", "bar", "baz")
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}
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