🌅

solutions/day9/day9.go

@@ -0,0 +1,153 @@
+package day9
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+)
+
+type Point struct {
+	x int
+	y int
+}
+
+func makeSnake(length int) []*Point {
+	snake := []*Point{}
+
+	for i := 0; i < length; i++ {
+		snake = append(snake, &Point{0, 0})
+	}
+
+	return snake
+}
+
+func move(direction rune, point *Point) {
+	switch direction {
+	case 'U':
+		point.y -= 1
+	case 'R':
+		point.x += 1
+	case 'D':
+		point.y += 1
+	case 'L':
+		point.x -= 1
+	default:
+		fmt.Println("PANIC! Bad direction", string(direction))
+	}
+}
+
+func abs(x int) int {
+	if x >= 0 {
+		return x
+	} else {
+		return -x
+	}
+}
+
+func areTouching(head *Point, tail *Point) bool {
+	return abs(head.x-tail.x) <= 1 && abs(head.y-tail.y) <= 1
+}
+
+func updateTail(head *Point, tail *Point) {
+	if areTouching(head, tail) {
+		return
+	}
+
+	if head.x == tail.x {
+		if head.y <= tail.y-2 {
+			tail.y -= 1
+			return
+		}
+
+		if head.y >= tail.y+2 {
+			tail.y += 1
+			return
+		}
+	}
+
+	if head.y == tail.y {
+		if head.x <= tail.x-2 {
+			tail.x -= 1
+			return
+		}
+		if head.x >= tail.x+2 {
+			tail.x += 1
+			return
+		}
+	}
+
+	proposedTails := []Point{
+		{tail.x - 1, tail.y - 1},
+		{tail.x - 1, tail.y + 1},
+		{tail.x + 1, tail.y - 1},
+		{tail.x + 1, tail.y + 1}}
+
+	for _, proposed := range proposedTails {
+		if areTouching(head, &proposed) {
+			tail.x = proposed.x
+			tail.y = proposed.y
+			return
+		}
+	}
+
+	fmt.Println("PANIC, couldn't figure out next step for", *head, "and", *tail)
+}
+
+func contains(array *[]Point, point Point) bool {
+	for _, val := range *array {
+		if val == point {
+			return true
+		}
+	}
+	return false
+}
+
+func runMove(direction rune, amount int, snake []*Point, visitedPoints *[]Point) {
+	for i := 0; i < amount; i++ {
+		move(direction, snake[0])
+		for t := 1; t < len(snake); t++ {
+			updateTail(snake[t-1], snake[t])
+		}
+		lastPoint := snake[len(snake)-1]
+		if !contains(visitedPoints, *lastPoint) {
+			*visitedPoints = append(*visitedPoints, *lastPoint)
+		}
+	}
+}
+
+func Run(filename string, lengthStr string) {
+	file, err := os.Open(filename)
+	if err != nil {
+		fmt.Println("Error opening file:", err)
+		return
+	}
+
+	snakeLength, err := strconv.Atoi(lengthStr)
+	if err != nil {
+		fmt.Println("Error parsing snake length:", err)
+		return
+	}
+
+	scanner := bufio.NewScanner(file)
+	scanner.Split(bufio.ScanLines)
+
+	snake := makeSnake(snakeLength)
+	visitedPoints := []Point{}
+
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		amount, err := strconv.Atoi(line[2:])
+		if err != nil {
+			fmt.Println("Could not parse argument", line)
+			return
+		}
+
+		runMove(rune(line[0]), amount, snake, &visitedPoints)
+	}
+
+	fmt.Println("The tail visited", len(visitedPoints), "points")
+
+	file.Close()
+}