AOC-2024/06/main.go

package main

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

const FILE_PATH = "./input.txt"

//const FILE_PATH = "./sample.txt"

func LoadInput(filename string) ([]string, error) {
	file, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer file.Close()

	var lines []string
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		lines = append(lines, scanner.Text())
	}

	if err := scanner.Err(); err != nil {
		return nil, err
	}

	return lines, nil
}

type Vector2 struct {
	x int
	y int
}

type structuredInput = [][]byte

func TransformInput(lines []string) structuredInput {
	var result = make([][]byte, 0)

	for _, line := range lines {
		result = append(result, []byte(line))
	}

	return result
}

const (
	UP    = iota
	RIGHT = iota
	DOWN  = iota
	LEFT  = iota
)

var MOVEMENTS = []Vector2{
	{0, -1},
	{1, 0},
	{0, 1},
	{-1, 0},
}

func addVectors(a Vector2, b Vector2) Vector2 {
	return Vector2{a.x + b.x, a.y + b.y}
}

func inBounds(point Vector2, limit Vector2) bool {
	return point.x >= 0 && point.x < limit.x && point.y >= 0 && point.y < limit.y
}

func Part1(input structuredInput) int {
	var result = 0

	var guard Vector2 = Vector2{}
	var direction int = UP
	var bounds Vector2 = Vector2{len(input[0]), len(input)}
	var visited [][]bool = make([][]bool, len(input))
	var next Vector2

	for i := range visited {
		visited[i] = make([]bool, len(input[i]))
	}

	for y := 0; y < len(input); y++ {
		for x := 0; x < len(input[y]); x++ {
			if input[y][x] == '^' {
				guard.x = x
				guard.y = y
			}
		}
	}

	visited[guard.y][guard.x] = true

	for inBounds(addVectors(guard, MOVEMENTS[direction]), bounds) {
		next = addVectors(guard, MOVEMENTS[direction])

		if input[next.y][next.x] == '#' {
			direction = (direction + 1) % 4
			continue
		}

		guard = next
		visited[guard.y][guard.x] = true
	}

	for i := range visited {
		for j := range visited[i] {
			if visited[i][j] {
				result++
			}
		}
	}

	return result
}

var visited [][][]bool

func generateVisited(bounds Vector2) {
	visited = make([][][]bool, 4)
	for i := range visited {
		visited[i] = make([][]bool, bounds.y)
		for j := range visited[i] {
			visited[i][j] = make([]bool, bounds.x)
		}
	}
}

func resetVisited() {
	for i := range visited {
		for j := range visited[i] {
			for m := range visited[i][j] {
				visited[i][j][m] = false
			}
		}
	}
}

func setPositionAsVisited(position Vector2, direction int) {
	visited[direction][position.y][position.x] = true
}

func hasVisited(position Vector2, direction int) bool {
	return visited[direction][position.y][position.x]
}

func checkForLoop(field [][]byte, startPosition Vector2, bounds Vector2) bool {
	var guard Vector2 = Vector2{startPosition.x, startPosition.y}
	var direction = UP
	var next Vector2

	resetVisited()

	setPositionAsVisited(guard, direction)

	for inBounds(addVectors(guard, MOVEMENTS[direction]), bounds) {
		next = addVectors(guard, MOVEMENTS[direction])

		if field[next.y][next.x] == '#' {
			direction = (direction + 1) % 4
			continue
		}

		guard = next

		if hasVisited(guard, direction) {
			return true
		}

		setPositionAsVisited(guard, direction)
	}

	return false
}

func Part2(input structuredInput) int {
	var result = 0
	var guard Vector2 = Vector2{}
	var bounds Vector2 = Vector2{len(input[0]), len(input)}

	generateVisited(bounds)

	for y := 0; y < len(input); y++ {
		for x := 0; x < len(input[y]); x++ {
			if input[y][x] == '^' {
				guard.x = x
				guard.y = y
			}
		}
	}

	for y := 0; y < len(input); y++ {
		for x := 0; x < len(input[y]); x++ {
			if input[y][x] == '.' {
				input[y][x] = '#'
				if checkForLoop(input, guard, bounds) {
					result++
				}
				input[y][x] = '.'
			}
		}
	}

	return result
}

func main() {
	var start time.Time
	var elapsed time.Duration = 0
	input, err := LoadInput(FILE_PATH)
	if err != nil {
		fmt.Println("Error loading input:", err)
		return
	}

	structuredInput := TransformInput(input)
	fmt.Println("Structured Input:", structuredInput)

	start = time.Now()
	fmt.Println("Solution Part 1: ", Part1(structuredInput))
	elapsed = time.Since(start)
	fmt.Printf("Part 1 took %s\n", elapsed)

	start = time.Now()
	fmt.Println("Solution Part 2: ", Part2(structuredInput))
	elapsed = time.Since(start)
	fmt.Printf("Part 2 took %s\n", elapsed)
}