AOC-2024/20/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
}

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

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

const (
	EMPTY = iota
	WALL  = iota
)

type Maze struct {
	field [][]int
	start Vector2
	end   Vector2
}

type structuredInput = Maze

func TransformInput(lines []string) structuredInput {
	var field = make([][]int, len(lines))
	var start Vector2
	var end Vector2

	for y := 0; y < len(lines); y++ {
		field[y] = make([]int, len(lines[y]))
		for x := 0; x < len(lines[y]); x++ {
			if lines[y][x] == '#' {
				field[y][x] = WALL
			} else {
				field[y][x] = EMPTY
			}

			if lines[y][x] == 'S' {
				start = Vector2{x, y}
			} else if lines[y][x] == 'E' {
				end = Vector2{x, y}
			}
		}
	}

	return Maze{field, start, end}
}

func getLowestIndex(score [][]int, poss []Vector2) int {
	var index = 0
	var value = score[poss[0].y][poss[0].x]

	for i := 1; i < len(poss); i++ {
		if score[poss[i].y][poss[i].x] < value {
			index = i
			value = score[poss[i].y][poss[i].x]
		}
	}

	return index
}

func findShortestLength(field [][]int, start Vector2, end Vector2) int {
	if start == end {
		return 0
	}

	var poss = []Vector2{start}
	var score = make([][]int, len(field))
	for y := 0; y < len(field); y++ {
		score[y] = make([]int, len(field[y]))
		for x := 0; x < len(field[y]); x++ {
			score[y][x] = -1
		}
	}
	score[start.y][start.x] = 0

	var index int
	var point Vector2
	var next Vector2
	for len(poss) > 0 {
		index = getLowestIndex(score, poss)
		point = poss[index]
		poss = append(poss[:index], poss[index+1:]...)

		for i := 0; i < 4; i++ {
			next = add(point, MOVEMENTS[i])
			if field[next.y][next.x] == EMPTY && score[next.y][next.x] == -1 {
				if next == end {
					return score[point.y][point.x] + 1
				}
				score[next.y][next.x] = score[point.y][point.x] + 1
				poss = append(poss, next)
			}
		}
	}

	return -1
}

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

	var baseSpeed = findShortestLength(input.field, input.start, input.end)
	var tempSpeed int

	for y := 1; y < len(input.field[y])-1; y++ {
		for x := 1; x < len(input.field[x])-1; x++ {
			if input.field[y][x] == WALL {
				input.field[y][x] = EMPTY
				tempSpeed = findShortestLength(input.field, input.start, input.end)

				if baseSpeed-tempSpeed >= 100 {
					result++
				}

				input.field[y][x] = WALL
			}
		}
	}

	return result
}

const RANGE = 20

func iabs(value int) int {
	if value < 0 {
		return value * -1
	}
	return value
}

func Part2(input structuredInput) int {
	var result = 0

	var baseSpeed = findShortestLength(input.field, input.start, input.end)

	var lengthToEnd = make([][]int, len(input.field))
	var lengthToPoint = make([][]int, len(input.field))

	for y := 0; y < len(input.field); y++ {
		lengthToEnd[y] = make([]int, len(input.field[y]))
		lengthToPoint[y] = make([]int, len(input.field[y]))
		for x := 0; x < len(input.field[y]); x++ {
			if input.field[y][x] == EMPTY {
				lengthToEnd[y][x] = findShortestLength(input.field, Vector2{x, y}, input.end)
				lengthToPoint[y][x] = findShortestLength(input.field, input.start, Vector2{x, y})
			}
		}
	}

	var speedToFinish int

	for y1 := 0; y1 < len(input.field); y1++ {
		for x1 := 0; x1 < len(input.field[y1]); x1++ {
			if input.field[y1][x1] == EMPTY {
				for y2 := max(y1-RANGE, 0); y2 < min(y1+RANGE+1, len(input.field)); y2++ {
					for x2 := max(x1-RANGE, 0); x2 < min(x1+RANGE+1, len(input.field[y2])); x2++ {
						if iabs(y2-y1)+iabs(x2-x1) <= RANGE && input.field[y2][x2] == EMPTY {
							speedToFinish = lengthToPoint[y1][x1] + iabs(y2-y1) + iabs(x2-x1) + lengthToEnd[y2][x2]
							if baseSpeed-speedToFinish >= 100 {
								result++
							}
						}
					}
				}
			}
		}
	}

	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)
}