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day10.go
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day10.go
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package main
import (
"fmt"
"math"
"os"
"sort"
"utils"
)
type coord struct {
X int
Y int
}
func (c coord) Distance(o coord) int {
return utils.Abs(utils.GCD(c.X-o.X, c.Y-o.Y))
}
func (c coord) Normalize(o coord) coord {
g := c.Distance(o)
return coord{(c.X - o.X) / g, (c.Y - o.Y) / g}
}
func (c coord) Atan2(o coord) float64 {
return math.Atan2(float64(c.X-o.X), float64(c.Y-o.Y))
}
func testCoord(asteroids []coord, a coord) int {
var visible []coord
for _, other := range asteroids {
if a == other {
continue
}
otherNorm := other.Normalize(a)
blocked := false
for _, b := range visible {
if otherNorm == b.Normalize(a) {
blocked = true
}
}
if !blocked {
visible = append(visible, other)
}
}
return len(visible)
}
func vaporize(asteroids []coord, laser coord) (last coord) {
sort.Slice(asteroids, func(i, j int) bool {
return asteroids[i].Atan2(laser) > asteroids[j].Atan2(laser)
})
var asteroidBins [][]coord
var bin []coord
currentBin := asteroids[0]
for _, a := range asteroids {
if a == laser {
continue
}
if currentBin.Normalize(laser) != a.Normalize(laser) {
sort.Slice(bin, func(i, j int) bool {
return bin[i].Distance(laser) < bin[j].Distance(laser)
})
asteroidBins = append(asteroidBins, bin)
bin = make([]coord, 0)
currentBin = a
}
bin = append(bin, a)
}
for i, j := 0, 0; i < 200; j = (j + 1) % len(asteroidBins) {
if len(asteroidBins[j]) > 0 {
last = asteroidBins[j][0]
asteroidBins[j] = asteroidBins[j][1:]
i++
}
}
return
}
func run(filepath string) (best coord, num int, last coord) {
data := utils.ReadFileToLines(filepath)
var asteroids []coord
for y := range data {
for x, pos := range data[y] {
if pos == '#' {
asteroids = append(asteroids, coord{x, y})
}
}
}
for _, a := range asteroids {
if res := testCoord(asteroids, a); res > num {
best = a
num = res
}
}
if len(asteroids) < 200 {
return
}
last = vaporize(asteroids, best)
return
}
func main() {
r1, r2, r3 := run(os.Args[1])
fmt.Println(r1)
fmt.Println(r2)
fmt.Println(r3)
}