mirror of
https://github.com/Luzifer/aoc2019.git
synced 2024-12-22 22:11:16 +00:00
214 lines
5 KiB
Go
214 lines
5 KiB
Go
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package aoc2019
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import (
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"io"
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"io/ioutil"
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"math"
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"os"
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"sort"
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"github.com/pkg/errors"
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)
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type day10MonitorGrid struct {
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asteroidMap []byte
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width int
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}
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func (d day10MonitorGrid) asteroidCount() int {
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var count int
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for _, c := range d.asteroidMap {
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if c == '#' {
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count++
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}
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}
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return count
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}
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func (d day10MonitorGrid) clone() *day10MonitorGrid {
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var grid = &day10MonitorGrid{asteroidMap: make([]byte, len(d.asteroidMap)), width: d.width}
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for i, c := range d.asteroidMap {
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grid.asteroidMap[i] = c
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}
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return grid
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}
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func (d day10MonitorGrid) getAsteroidPositions() []int {
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var knownPositions []int
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for i, c := range d.asteroidMap {
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if c != '#' {
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// Not an asteroid, don't care
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continue
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}
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knownPositions = append(knownPositions, i)
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}
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return knownPositions
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}
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func (d day10MonitorGrid) getCleanedGrid(x, y int) *day10MonitorGrid {
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// Clone the map to work on
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var grid = d.clone()
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// Collect positions of all known asteroids
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var knownPositions = grid.getAsteroidPositions()
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// Mark observer (does not count into observable asteroids)
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grid.asteroidMap[grid.coordToPos(x, y)] = '@'
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// Iterate all positions and remove covered (invisible) asteroids
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for _, pos := range knownPositions {
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var aX, aY = d.posToCoord(pos)
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if grid.isObstructed(x, y, aX, aY) {
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grid.asteroidMap[pos] = '-'
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}
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}
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return grid
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}
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func (d *day10MonitorGrid) isObstructed(observX, observY, x, y int) bool {
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var distX, distY = x - observX, y - observY
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if distX == 0 && distY == 0 {
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// No steps, observer equals asteroid, needless calculation
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return false
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}
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var (
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div = int(math.Abs(float64(greatestCommonDivisor(int64(distX), int64(distY)))))
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stepX, stepY = distX / div, distY / div
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)
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for i := 1; i < math.MaxInt64; i++ {
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var rPosX, rPosY = observX + stepX*i, observY + stepY*i
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if rPosX < 0 || rPosX >= d.width || rPosY < 0 || rPosY >= len(d.asteroidMap)/d.width {
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// Position outside grid, stop searching
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panic(errors.Errorf("Observed position ran out of bounds (obsX=%d obsY=%d x=%d y=%d div=%d stepX=%d stepY=%d)", observX, observY, x, y, div, stepX, stepY))
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}
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if rPosX == x && rPosY == y {
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return false
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}
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if d.asteroidMap[d.coordToPos(rPosX, rPosY)] == '#' {
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return true
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}
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}
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panic(errors.Errorf("Unreachable end was reached"))
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}
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func (d day10MonitorGrid) coordToPos(x, y int) int { return y*d.width + x }
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func (d day10MonitorGrid) posToCoord(pos int) (int, int) { return pos % d.width, pos / d.width }
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func (d day10MonitorGrid) step2deg(x, y int) float64 {
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rad := math.Atan2(float64(x), float64(y))
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deg := rad * (180 / math.Pi)
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return 180 + -1*deg
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}
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func day10ReadAsteroidMap(in io.Reader) (*day10MonitorGrid, error) {
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var grid = &day10MonitorGrid{}
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raw, err := ioutil.ReadAll(in)
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if err != nil {
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return nil, errors.Wrap(err, "Unable to read asteroid map")
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}
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for _, c := range raw {
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if c == '\n' {
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if grid.width == 0 {
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grid.width = len(grid.asteroidMap)
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}
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// Skip newlines for our representation
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continue
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}
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grid.asteroidMap = append(grid.asteroidMap, c)
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}
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return grid, nil
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}
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func solveDay10Part1Coordinate(inFile string) (*day10MonitorGrid, int, error) {
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f, err := os.Open(inFile)
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if err != nil {
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return nil, 0, errors.Wrap(err, "Unable to open input file")
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}
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defer f.Close()
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grid, err := day10ReadAsteroidMap(f)
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if err != nil {
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return nil, 0, errors.Wrap(err, "Unable to read asteroid map")
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}
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var (
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bestMonitorPos int
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bestAsteroidCount int
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)
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for _, pos := range grid.getAsteroidPositions() {
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var aX, aY = grid.posToCoord(pos)
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rGrid := grid.getCleanedGrid(aX, aY)
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if c := rGrid.asteroidCount(); c > bestAsteroidCount {
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bestMonitorPos = pos
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bestAsteroidCount = c
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}
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}
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return grid, bestMonitorPos, nil
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}
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func solveDay10Part1(inFile string) (int, error) {
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grid, bestMonitorPos, err := solveDay10Part1Coordinate(inFile)
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if err != nil {
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return 0, err
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}
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var aX, aY = grid.posToCoord(bestMonitorPos)
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return grid.getCleanedGrid(aX, aY).asteroidCount(), nil
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}
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func solveDay10Part2(inFile string) (int, error) {
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grid, bestMonitorPos, err := solveDay10Part1Coordinate(inFile)
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if err != nil {
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return 0, err
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}
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var (
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mX, mY = grid.posToCoord(bestMonitorPos)
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destroyed []int
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)
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// Mark monitor / laser -- cannot be destroyed
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grid.asteroidMap[bestMonitorPos] = 'M'
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// Gradually destroy asteroids
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for grid.asteroidCount() > 0 {
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asteroidsInSight := grid.getCleanedGrid(mX, mY).getAsteroidPositions()
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var degPos [][2]int
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for _, pos := range asteroidsInSight {
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var aX, aY = grid.posToCoord(pos)
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degPos = append(degPos, [2]int{
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pos,
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int(grid.step2deg(aX-mX, aY-mY) * 1000000), // Degree to asteroid in 6-digit precision
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})
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}
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// Sort by degree low-to-high -- represents order of destruction
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sort.Slice(degPos, func(i, j int) bool { return degPos[i][1] < degPos[j][1] })
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for _, dp := range degPos {
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grid.asteroidMap[dp[0]] = '*' // Mark asteroids destroyed
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destroyed = append(destroyed, dp[0])
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}
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}
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destr200X, destr200Y := grid.posToCoord(destroyed[199])
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return 100*destr200X + destr200Y, nil
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}
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