AdventOfCode2022/09/main.go

package main

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

func mustAtoi(line string) int {
	i, _ := strconv.Atoi(line)
	return i
}

func main() {
	start := time.Now()
	partOne()
	duration := time.Since(start)
	partTwo()
	duration2 := time.Since(start)
	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
}

func makeScanner(test bool) *bufio.Scanner {
	var f *os.File
	if test {
		f, _ = os.Open("inputs/testinput")
	} else {
		f, _ = os.Open("inputs/input")
	}
	reader := bufio.NewReader(f)
	return bufio.NewScanner(reader)
}

type coord struct {
	x int
	y int
}

func moveNextKnot(parent, child *coord) {
	if parent.y-child.y == 2 {
		child.y++
		if parent.x-child.x == 2 {
			child.x++
		} else if child.x-parent.x == 2 {
			child.x--
		} else {
			child.x = parent.x
		}
	}
	if child.y-parent.y == 2 {
		child.y--
		if parent.x-child.x == 2 {
			child.x++
		} else if child.x-parent.x == 2 {
			child.x--
		} else {
			child.x = parent.x
		}
	}
	if parent.x-child.x == 2 {
		child.x++
		if parent.y-child.y == 2 {
			child.y++
		} else if child.y-parent.y == 2 {
			child.y--
		} else {
			child.y = parent.y
		}
	}
	if child.x-parent.x == 2 {
		child.x--
		if parent.y-child.y == 2 {
			child.y++
		} else if child.y-parent.y == 2 {
			child.y--
		} else {
			child.y = parent.y
		}
	}
}

func displayGrid(rope []coord) {
	for x := 0; x < 10; x++ {
		for y := 0; y < 10; y++ {
			printed := false
			for k, c := range rope {
				if c.x == x && c.y == y && !printed {
					printed = true
					if k == 0 {
						fmt.Print("H")
					} else {
						fmt.Print(k)
					}
				}
			}
			if !printed {
				fmt.Print(".")
			}
		}
		fmt.Println()
	}
}

func partOne() {
	scanner := makeScanner(false)

	grid := map[coord]bool{{x: 0, y: 0}: true}
	head := coord{x: 0, y: 0}
	tail := coord{x: 0, y: 0}

	for scanner.Scan() {
		line := scanner.Text()
		l := strings.Split(line, " ")
		direction, steps := l[0], mustAtoi(l[1])
		for i := 0; i < steps; i++ {
			switch direction {
			case "U":
				head.y++
			case "D":
				head.y--
			case "L":
				head.x--
			case "R":
				head.x++
			default:
				panic("oh no")
			}
			moveNextKnot(&head, &tail)
			grid[tail] = true
		}
	}
	fmt.Println(len(grid))
}

func partTwo() {
	scanner := makeScanner(false)

	grid := map[coord]bool{{x: 0, y: 0}: true}
	rope := []coord{
		{x: 0, y: 0},
		{x: 0, y: 0},
		{x: 0, y: 0},
		{x: 0, y: 0},
		{x: 0, y: 0},
		{x: 0, y: 0},
		{x: 0, y: 0},
		{x: 0, y: 0},
		{x: 0, y: 0},
		{x: 0, y: 0},
	}

	for scanner.Scan() {
		line := scanner.Text()
		l := strings.Split(line, " ")
		direction, steps := l[0], mustAtoi(l[1])
		for i := 0; i < steps; i++ {
			switch direction {
			case "U":
				rope[0].y++
			case "D":
				rope[0].y--
			case "L":
				rope[0].x--
			case "R":
				rope[0].x++
			default:
				panic("oh no")
			}
			for i := 0; i < 9; i++ {
				moveNextKnot(&rope[i], &rope[i+1])
			}
			grid[rope[9]] = true
		}
	}
	fmt.Println(len(grid))
}