adventofcode/2024/day15/main.go

package main

import (
	"fmt"

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

func main() {
	inp := h.StdinToStringSlice()
	part1(inp)
	fmt.Println()
	part2(inp)
}

func part1(inp []string) {
	fmt.Println("# Part 1")
	m, dirs := parseInput(inp)
	for i := range dirs {
		bot, _ := m.FindFirst('@')
		move(m, bot, dirs[i])
	}
	crates := m.FindAll('O')
	var total int
	for i := range crates {
		add := (crates[i].Y*100 + crates[i].X)
		total = total + add
	}
	fmt.Println("GPS Sum:", total)
}

func part2(inp []string) {
	fmt.Println("# Part 2")
	m, dirs := parseInput2(inp)
	for i := range dirs {
		bot, _ := m.FindFirst('@')
		move(m, bot, dirs[i])
	}
	crates := m.FindAll('[')
	var total int
	for i := range crates {
		add := (crates[i].Y*100 + crates[i].X)
		total = total + add
	}
	fmt.Println("GPS Sum:", total)
}

func move(m h.CoordByteMap, orig h.Coordinate, dir byte) bool {
	if !canMove(m, orig, dir) {
		return false
	}
	oB := m.Get(orig)
	if dir == '^' || dir == 'v' {
		switch oB {
		case ']':
			return moveCrate(m, orig.West(), dir)
		case '[':
			return moveCrate(m, orig, dir)
		}
	}
	var moveTo h.Coordinate
	switch dir {
	case '^':
		moveTo = orig.North()
	case '>':
		moveTo = orig.East()
	case 'v':
		moveTo = orig.South()
	case '<':
		moveTo = orig.West()
	}
	dest := m.Get(moveTo)
	if dest == '#' {
		// A wall, can't move
		return false
	} else if dest != '.' {
		// Not a wall, but not empty, can we push it?
		if !move(m, moveTo, dir) {
			return false
		}
		// Fall through
	}
	m.Put(moveTo, oB)
	m.Put(orig, '.')
	return true
}

func moveCrate(m h.CoordByteMap, orig h.Coordinate, dir byte) bool {
	if !canMoveCrate(m, orig, dir) {
		return false
	}
	var moveTo h.Coordinate
	switch dir {
	case '^':
		moveTo = orig.North()
	case 'v':
		moveTo = orig.South()
	}
	destW, destE := m.Get(moveTo), m.Get(moveTo.East())
	if destW == '#' || destE == '#' {
		// A wall, can't move
		return false
	} else {
		if destW != '.' && !move(m, moveTo, dir) {
			return false
		}
		// Check other half of crate
		if (destE != '.' && destE != ']') && !move(m, moveTo.East(), dir) {
			return false
		}
		// Fall through
	}
	m.Put(moveTo, '[')
	m.Put(moveTo.East(), ']')
	m.Put(orig, '.')
	m.Put(orig.East(), '.')
	return true
}

func canMove(m h.CoordByteMap, orig h.Coordinate, dir byte) bool {
	oB := m.Get(orig)
	if dir == '^' || dir == 'v' {
		switch oB {
		case ']':
			return canMoveCrate(m, orig.West(), dir)
		case '[':
			return canMoveCrate(m, orig, dir)
		}
	}
	var moveTo h.Coordinate
	switch dir {
	case '^':
		moveTo = orig.North()
	case '>':
		moveTo = orig.East()
	case 'v':
		moveTo = orig.South()
	case '<':
		moveTo = orig.West()
	}
	dest := m.Get(moveTo)
	if dest == '#' {
		// A wall, can't move
		return false
	} else if dest != '.' {
		// Not a wall, but not empty, can we push it?
		if !canMove(m, moveTo, dir) {
			return false
		}
		// Fall through
	}
	// can move
	return true
}

func canMoveCrate(m h.CoordByteMap, orig h.Coordinate, dir byte) bool {
	var moveTo h.Coordinate
	switch dir {
	case '^':
		moveTo = orig.North()
	case 'v':
		moveTo = orig.South()
	}
	destW, destE := m.Get(moveTo), m.Get(moveTo.East())

	if destW == '#' || destE == '#' {
		// A wall, can't move
		return false
	} else {
		if destW != '.' && !canMove(m, moveTo, dir) {
			return false
		}
		// Check other half of crate
		if destE != '.' && !canMove(m, moveTo.East(), dir) {
			return false
		}
		// Fall through
	}
	// can move
	return true
}

func parseInput(inp []string) (h.CoordByteMap, []byte) {
	var m h.CoordByteMap
	var dirs []byte
	var inDirs bool
	for i := range inp {
		if inDirs {
			dirs = append(dirs, []byte(inp[i])...)
		} else {
			if inp[i] == "" {
				m = h.StringSliceToCoordByteMap(inp[:i])
				inDirs = true
			}
		}
	}
	return m, dirs
}

func parseInput2(inp []string) (h.CoordByteMap, []byte) {
	// First modify the input
	var m h.CoordByteMap
	var newMap []string
	var inDirs bool
	var dirs []byte
	for i := range inp {
		if inDirs {
			dirs = append(dirs, []byte(inp[i])...)
		} else {
			if inp[i] == "" {
				m = h.StringSliceToCoordByteMap(newMap)
				inDirs = true
			}
			var newLine []byte
			for j := range inp[i] {
				switch inp[i][j] {
				case 'O':
					newLine = append(newLine, []byte{'[', ']'}...)
				case '@':
					newLine = append(newLine, []byte{'@', '.'}...)
				default:
					newLine = append(newLine, []byte{inp[i][j], inp[i][j]}...)
				}
			}
			newMap = append(newMap, string(newLine))
		}
	}
	return m, dirs
}