adventofcode/2021/day19/main.go

package main

import (
	"errors"
	"fmt"
	"os"
	"strings"

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

func main() {
	inp := h.StdinToStringSlice()

	ans1, ans2 := solve(inp)
	fmt.Println("# Part 1")
	fmt.Println(ans1)
	fmt.Println()
	fmt.Println("# Part 2")
	fmt.Println(ans2)
}

func solve(input []string) (int, int) {
	scanners := parseScanners(input)

	solved := []Scanner{scanners[0]}
	solved[0].absoluteCoords = solved[0].relativeCoords
	solved[0].fillAbsMap()

	// Scanners with a position we don't know yet
	unk := scanners[1:]
	// loop until we know them all
	for len(unk) > 0 {
		fmt.Print(h.CLEAR_SCREEN, "Processing...\n")
		c, t := len(solved), len(scanners)
		h.PrintProgress(c, t)
		fmt.Printf(" %d/%d %d%%\n", c, t, int(float64(c)/float64(t)*100))

		for i, undet := range unk {
			ok := undet.findCoords(solved)
			if ok {
				solved = append(solved, undet)
				// remove the determined scanner from the unknown list
				copy(unk[i:], unk[i+1:])
				unk = unk[:len(unk)-1]
				break
			}
		}
	}

	allBeacons := map[[3]int]bool{}
	for _, s := range solved {
		for c := range s.absoluteCoordsMap {
			allBeacons[c] = true
		}
	}

	var furthest int
	for i, s1 := range solved {
		for j, s2 := range solved {
			if i == j {
				continue
			}
			dist := h.Abs(s1.x-s2.x) + h.Abs(s1.y-s2.y) + h.Abs(s1.z-s2.z)
			if dist > furthest {
				furthest = dist
			}
		}
	}
	return len(allBeacons), furthest
}

func parseScanners(inp []string) []Scanner {
	var scanners []Scanner
	for i := range inp {
		if strings.HasPrefix(inp[i], "---") {
			end := i
			for ; end < len(inp); end++ {
				if inp[end] == "" {
					break
				}
			}
			wrk, err := NewScannerFromInput(inp[i:end])
			if err == nil {
				scanners = append(scanners, wrk)
			} else {
				fmt.Println("Error parsing scanners")
				os.Exit(1)
			}
		}
	}
	return scanners
}

type Scanner struct {
	number            int
	x, y, z           int
	relativeCoords    [][3]int
	rotations         [][][3]int
	absoluteCoords    [][3]int
	absoluteCoordsMap map[[3]int]bool
}

func NewScannerFromInput(inp []string) (Scanner, error) {
	s := Scanner{
		absoluteCoordsMap: make(map[[3]int]bool),
	}
	r := strings.NewReader(inp[0])
	_, err := fmt.Fscanf(r, "--- scanner %d ---", &s.number)
	if err != nil {
		return s, errors.New("No Scanner ID")
	}
	for _, v := range inp[1:] {
		var x, y, z int
		r = strings.NewReader(v)
		_, err := fmt.Fscanf(r, "%d,%d,%d", &x, &y, &z)
		if err != nil {
			return s, err
		}
		s.relativeCoords = append(s.relativeCoords, [3]int{x, y, z})
	}
	s.fillRotations()
	return s, nil
}

func (s *Scanner) fillAbsMap() {
	s.absoluteCoordsMap = map[[3]int]bool{}
	if len(s.absoluteCoords) == 0 {
		panic(fmt.Sprintf("absolute coords not set for scanner %d", s.number))
	}
	for _, ac := range s.absoluteCoords {
		s.absoluteCoordsMap[ac] = true
	}
}

// Fill in all coordinates for all beacon rotations
func (s *Scanner) fillRotations() {
	dir1 := s.relativeCoords
	var dir2, dir3, dir4, dir5, dir6 [][3]int
	for _, c := range dir1 {
		x, y, z := c[0], c[1], c[2]
		dir2 = append(dir2, [3]int{x, -y, -z})
		dir3 = append(dir3, [3]int{x, -z, y})
		dir4 = append(dir4, [3]int{-y, -z, x})
		dir5 = append(dir5, [3]int{-x, -z, -y})
		dir6 = append(dir6, [3]int{y, -z, -x})
	}
	sixRotations := [][][3]int{
		dir1, dir2,
		dir3, dir4,
		dir5, dir6,
	}

	var finalRotations [][][3]int
	for _, rotation := range sixRotations {
		var r2, r3, r4 [][3]int
		for _, c := range rotation {
			x, y, z := c[0], c[1], c[2]
			r2 = append(r2, [3]int{-y, x, z})
			r3 = append(r3, [3]int{-x, -y, z})
			r4 = append(r4, [3]int{y, -x, z})
		}
		finalRotations = append(finalRotations, rotation, r2, r3, r4)
	}
	s.rotations = finalRotations
}

// Find the absolute coordinates for this scanner, if we can.
func (s *Scanner) findCoords(solved []Scanner) bool {
	for _, rotatedCoords := range s.rotations {
		for _, set := range solved {
			for _, absCoord := range set.absoluteCoords {
				for _, relativeCoord := range rotatedCoords {
					unsolvedAbsoluteCoords := fillAbsCoords(absCoord, relativeCoord, rotatedCoords)

					var matchingCount int
					for _, ac := range unsolvedAbsoluteCoords {
						if set.absoluteCoordsMap[ac] {
							matchingCount++
						}
					}

					if matchingCount >= 12 {
						s.relativeCoords = rotatedCoords
						s.absoluteCoords = unsolvedAbsoluteCoords
						s.fillAbsMap()
						s.x = absCoord[0] - relativeCoord[0]
						s.y = absCoord[1] - relativeCoord[1]
						s.z = absCoord[2] - relativeCoord[2]
						return true
					}
				}
			}
		}
	}
	return false
}

// Assume that absolute and relative are actually the same coordinate, calc the diff of all relative Coords
func fillAbsCoords(absolute, relative [3]int, relativeCoords [][3]int) [][3]int {
	diff := [3]int{
		absolute[0] - relative[0],
		absolute[1] - relative[1],
		absolute[2] - relative[2],
	}

	var absCoords [][3]int
	for _, c := range relativeCoords {
		absCoords = append(absCoords, [3]int{
			diff[0] + c[0],
			diff[1] + c[1],
			diff[2] + c[2],
		})
	}

	return absCoords
}