adventofcode/2024/day06/main.go

package main

import (
	"fmt"
	"time"

	h "git.bullercodeworks.com/brian/adventofcode/helpers"
)

func main() {
	inp := h.StdinToCoordMap()
	cp := inp.Copy()
	m := part1(inp)
	part2(*cp, m.FindAll('X'))
}

var debug = false

func part1(m h.CoordByteMap) h.CoordByteMap {
	init, err := m.FindFirst('^')
	h.CheckErr(err)
	for moveGuard(m) {
		if debug {
			fmt.Println(h.CLEAR_SCREEN)
			fmt.Println(m)
			guard := m.FindAll('^', '>', 'v', '<')[0]
			fmt.Println(guard)
			time.Sleep(time.Second / 10)
		}
	}
	fmt.Println()
	fmt.Println("# Part 1")
	fmt.Printf("Guard moved into %d positions.\n", m.Count('X'))
	fmt.Println()
	m.Put(init, '^')
	return m
}

func part2(clean h.CoordByteMap, p []h.Coordinate) {
	// m should have all of the 'X' spots where the guard moved in part 1
	init, err := clean.FindFirst('^')
	h.CheckErr(err)
	var obstacles []h.Coordinate
	for i := range p {
		fmt.Println(h.CLEAR_SCREEN)
		fmt.Print("Progress: ")
		h.PrintProgress(i, len(p))
		fmt.Printf(" %d/%d\n", i, len(p))
		m := *clean.Copy()
		// Try putting an obstacle at p[i]
		m.Put(p[i], 'O')
		history := make(map[h.Coordinate][]string)
		guard := m.FindAll('^', '>', 'v', '<')[0]
		tst := m.Get(guard)
		history[guard] = append(history[guard], string(tst))
		var foundLoop bool
		for moveGuard(m) && !foundLoop {
			// fmt.Print(".")
			if debug {
				fmt.Println(h.CLEAR_SCREEN)
				fmt.Println(m)
				guard := m.FindAll('^', '>', 'v', '<')[0]
				fmt.Printf("Guard: %s - Testing Obstacle: %s\n", guard, p[i])
				fmt.Println(obstacles)
				fmt.Println(history)
				time.Sleep(time.Second / 10)
			}
			guard := m.FindAll('^', '>', 'v', '<')[0]
			bt := m.Get(guard)
			// Check if we already have this position/orientation in our history
			for j := range history[guard] {
				if history[guard][j] == string(bt) {
					if !contains(obstacles, p[i]) {
						obstacles = append(obstacles, p[i])
						foundLoop = true
						if debug {
							fmt.Println("Found Loop:", string(history[guard][j]), "==", string(bt))
						}
						break
					}
				}
			}
			history[guard] = append(history[guard], string(bt))
		}
		m.Put(p[i], '.')
		m.Put(init, '^')
	}
	fmt.Println()
	fmt.Println("# Part 2")
	fmt.Printf("Obstacle positions to create a loop: %d\n", len(obstacles))
	// 583 is too low
}

func checkForLoop(m h.CoordByteMap) {
}

func contains(sl []h.Coordinate, c h.Coordinate) bool {
	for i := range sl {
		if sl[i].Equals(c) {
			return true
		}
	}
	return false
}

func turn(g byte) byte {
	switch g {
	case '^':
		return '>'
	case '>':
		return 'v'
	case 'v':
		return '<'
	default:
		return '^'
	}
}

func nextPos(guard h.Coordinate, m h.CoordByteMap) h.Coordinate {
	switch m.Get(guard) {
	case '>':
		return guard.East()
	case 'v':
		return guard.South()
	case '<':
		return guard.West()
	}
	return guard.North()
}

func moveGuard(m h.CoordByteMap) bool {
	guard := m.FindAll('^', '>', 'v', '<')[0]
	currBt := m.Get(guard)
	turn := turn(currBt)
	next := nextPos(guard, m)
	if !m.ContainsCoord(next) {
		m.Put(guard, 'X')
		return false
	}
	tst := m.Get(next)
	if tst == '#' || tst == 'O' {
		m.Put(guard, turn)
		return moveGuard(m)
	}
	m.Put(guard, 'X')
	m.Put(next, currBt)
	return true
}