adventofcode/2022/day18/main.go

package main

import (
	"fmt"
	"math"
	"strings"

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

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

func part1(inp []string) {
	scan := ParseSurface(inp)
	var surface int
	for k := range scan {
		for _, chk := range []pos{k.Top(), k.Bottom(), k.Left(), k.Right(), k.Front(), k.Back()} {
			if _, ok := scan[chk]; !ok {
				surface++
			}
		}
	}
	fmt.Println("# Part 1")
	fmt.Println("Surface Area:", surface)
}
func part2(inp []string) {
	scan := ParseCubes(inp)
	scanExternal(scan)

	var surface int
	for _, cb := range scan {
		if cb.top == nil && !cb.topInt {
			surface++
		}
		if cb.bottom == nil && !cb.bottomInt {
			surface++
		}
		if cb.right == nil && !cb.rightInt {
			surface++
		}
		if cb.left == nil && !cb.leftInt {
			surface++
		}
		if cb.front == nil && !cb.frontInt {
			surface++
		}
		if cb.back == nil && !cb.backInt {
			surface++
		}
	}
	fmt.Println("# Part 2")
	fmt.Println("External Surface Area:", surface)
}

func scanExternal(m map[pos]*cube) {
	min := pos{x: math.MaxInt, y: math.MaxInt, z: math.MaxInt}
	max := pos{x: math.MinInt, y: math.MinInt, z: math.MinInt}
	for k := range m {
		min.x = h.Min(min.x, k.x)
		min.y = h.Min(min.y, k.y)
		min.z = h.Min(min.z, k.z)
		max.x = h.Max(max.x, k.x)
		max.y = h.Max(max.y, k.y)
		max.z = h.Max(max.z, k.z)
	}
	edges := make(map[pos]bool)
	for z := min.z - 1; z < max.z+1; z++ {
		for y := min.y - 1; y < max.y+1; y++ {
			for x := min.x - 1; x < max.x+1; x++ {
				edges[pos{min.x, y, z}] = true
				edges[pos{x, min.y, z}] = true
				edges[pos{x, y, min.z}] = true
				edges[pos{max.x, y, z}] = true
				edges[pos{x, max.y, z}] = true
				edges[pos{x, y, max.z}] = true
			}
		}
	}
	for k, v := range m {
		if v.left == nil && !canPath(k.Left(), edges, m) {
			v.leftInt = true
		}
		if v.right == nil && !canPath(k.Right(), edges, m) {
			v.rightInt = true
		}
		if v.top == nil && !canPath(k.Top(), edges, m) {
			v.topInt = true
		}
		if v.bottom == nil && !canPath(k.Bottom(), edges, m) {
			v.bottomInt = true
		}
		if v.front == nil && !canPath(k.Front(), edges, m) {
			v.frontInt = true
		}
		if v.back == nil && !canPath(k.Back(), edges, m) {
			v.backInt = true
		}
	}
}

func canPath(from pos, to map[pos]bool, scan map[pos]*cube) bool {
	queue := []pos{from}
	visit := make(map[pos]bool)
	result := false
	for len(queue) > 0 {
		cur := queue[0]
		queue = queue[1:]
		if _, ok := to[cur]; ok {
			result = true
			break
		}
		if _, ok := visit[cur]; ok {
			continue
		}
		visit[cur] = true
		moves := []pos{
			cur.Top(), cur.Bottom(),
			cur.Left(), cur.Right(),
			cur.Front(), cur.Back(),
		}
		for _, mv := range moves {
			if _, ok := scan[mv]; ok {
				continue
			}
			queue = append(queue, mv)
		}
	}
	return result
}

func ParseSurface(inp []string) map[pos]bool {
	m := make(map[pos]bool)
	for i := range inp {
		pts := strings.Split(inp[i], ",")
		m[pos{
			x: h.Atoi(pts[0]),
			y: h.Atoi(pts[1]),
			z: h.Atoi(pts[2]),
		}] = true
	}
	return m
}
func ParseCubes(inp []string) map[pos]*cube {
	m := make(map[pos]*cube)
	for i := range inp {
		pts := strings.Split(inp[i], ",")
		pos := pos{
			x: h.Atoi(pts[0]),
			y: h.Atoi(pts[1]),
			z: h.Atoi(pts[2]),
		}
		m[pos] = &cube{position: pos}
	}
	for k, v := range m {
		if _, ok := m[k.Top()]; ok {
			m[k.Top()].bottom = v
			v.top = m[k.Top()]
		}
		if _, ok := m[k.Bottom()]; ok {
			m[k.Bottom()].top = v
			v.bottom = m[k.Bottom()]
		}
		if _, ok := m[k.Left()]; ok {
			m[k.Left()].right = v
			v.left = m[k.Left()]
		}
		if _, ok := m[k.Right()]; ok {
			m[k.Right()].left = v
			v.right = m[k.Right()]
		}
		if _, ok := m[k.Front()]; ok {
			m[k.Front()].back = v
			v.front = m[k.Front()]
		}
		if _, ok := m[k.Back()]; ok {
			m[k.Back()].front = v
			v.back = m[k.Back()]
		}
	}
	return m
}

type pos struct{ x, y, z int }

func (p pos) Top() pos    { return pos{x: p.x, y: p.y + 1, z: p.z} }
func (p pos) Bottom() pos { return pos{x: p.x, y: p.y - 1, z: p.z} }
func (p pos) Left() pos   { return pos{x: p.x - 1, y: p.y, z: p.z} }
func (p pos) Right() pos  { return pos{x: p.x + 1, y: p.y, z: p.z} }
func (p pos) Front() pos  { return pos{x: p.x, y: p.y, z: p.z - 1} }
func (p pos) Back() pos   { return pos{x: p.x, y: p.y, z: p.z + 1} }

type cube struct {
	position    pos
	top, bottom *cube
	front, back *cube
	left, right *cube

	topInt, bottomInt bool
	frontInt, backInt bool
	leftInt, rightInt bool
}