commit b585df7d57594a820b99444d7f420891e2d75e6c
parent 41df761c54d3c40adbdeab70554cffb38d5e67c2
Author: Shimmy Xu <shimmy.xu@shimmy1996.com>
Date: Thu, 24 Dec 2020 18:12:00 -0600
Add 2020 day 24
Diffstat:
| A | 2020/day24/input.txt | | | 450 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ |
| A | 2020/day24/main.go | | | 135 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ |
2 files changed, 585 insertions(+), 0 deletions(-)
diff --git a/2020/day24/input.txt b/2020/day24/input.txt
@@ -0,0 +1,450 @@
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+wseeweneneweseeneeneneeeseenenene
+neesenwwsenenenewwweeneneweesw
+nesesenwneeneeesenwwswneswnwnwneww
+eesweweneeneeeeneesweeseenwe
+nenwnwnwswneneenenenwnenwnwnwswnesenenenew
+neswnesenwswseswesenwswseswewswsesww
+eseenweeseeeeeeesesesenwswee
+wseseeseseeesesee
+swsewnewwwnesesewwwwnwsewnenewnw
+nenenenenesenenenenewnwnesenenenwnw
+nwswswnewewnenwsewseswwsenenwesenwew
+enwnwnwwnwswwwnww
+eeeseeeesesenewseweeeeesene
+nwnwnewwwnwenwwswwnwwnwseesewse
+weenenenenenenenewnenesweneenesenw
+swenwsesenenwsewswnewsw
+senenwneseswwswnesenwnewnenenenenenenenw
+wwswwwswwnewwsewsw
+enewswwnewwwwwwnewnwseswswwwsw
diff --git a/2020/day24/main.go b/2020/day24/main.go
@@ -0,0 +1,135 @@
+package main
+
+import (
+ "bufio"
+ "fmt"
+ "os"
+ "regexp"
+)
+
+const (
+ E = iota
+ SE
+ SW
+ W
+ NW
+ NE
+ WHITE = 0
+ BLACK = 1
+)
+
+type pos [2]int
+
+func (this pos) move(dir int) pos {
+ other := pathToCoord([]int{dir})
+ return pos{this[0] + other[0], this[1] + other[1]}
+}
+
+func readInput(filename string) (res [][]int) {
+ file, _ := os.Open(filename)
+ defer file.Close()
+
+ scanner := bufio.NewScanner(file)
+ matcher := regexp.MustCompile(`e|se|sw|w|nw|ne`)
+ dirMap := map[string]int{
+ "e": E, "se": SE, "sw": SW, "w": W, "nw": NW, "ne": NE,
+ }
+ for scanner.Scan() {
+ curr := []int{}
+ for _, dir := range matcher.FindAllStringSubmatch(scanner.Text(), -1) {
+ curr = append(curr, dirMap[dir[0]])
+ }
+ res = append(res, curr)
+ }
+ return
+}
+
+func main() {
+ input := readInput("./input.txt")
+ // 382
+ fmt.Println(part1(input))
+ // 3964
+ fmt.Println(part2(input))
+}
+
+func pathToCoord(path []int) (coord pos) {
+ // Use E/W axis as x, NW/SE axis as y.
+ for _, dir := range path {
+ switch dir {
+ case E, NE:
+ coord[0] += 1
+ case W, SW:
+ coord[0] -= 1
+ }
+ switch dir {
+ case NW, NE:
+ coord[1] += 1
+ case SE, SW:
+ coord[1] -= 1
+ }
+ }
+ return
+}
+
+func part1(input [][]int) (blackCount int) {
+ tileColor := map[pos]int{}
+ for _, path := range input {
+ coord := pathToCoord(path)
+ tileColor[coord] = 1 - tileColor[coord]
+ }
+ for _, v := range tileColor {
+ if v == BLACK {
+ blackCount += 1
+ }
+ }
+ return
+}
+
+func flip(tileColor map[pos]int, steps int) map[pos]int {
+ // Same as day 17.
+ curr, next := tileColor, map[pos]int{}
+ for i := 0; i < steps; i++ {
+ // Update neighbor black count.
+ next = map[pos]int{}
+ for p, v := range curr {
+ next[p] = next[p] // ensure key exists
+ for _, dir := range []int{E, SE, SW, W, NW, NE} {
+ next[p.move(dir)] += v
+ }
+ }
+ // Update state.
+ for p, blackCount := range next {
+ switch curr[p] {
+ case BLACK:
+ if blackCount == 0 || blackCount > 2 {
+ next[p] = WHITE
+ } else {
+ next[p] = BLACK
+ }
+ case WHITE:
+ if blackCount == 2 {
+ next[p] = BLACK
+ } else {
+ next[p] = WHITE
+ }
+ }
+ }
+ curr = next
+ }
+ return curr
+}
+
+func part2(input [][]int) (blackCount int) {
+ tileColor := map[pos]int{}
+ for _, path := range input {
+ coord := pathToCoord(path)
+ tileColor[coord] = 1 - tileColor[coord]
+ }
+ tileColor = flip(tileColor, 100)
+ for _, v := range tileColor {
+ if v == BLACK {
+ blackCount += 1
+ }
+ }
+ return
+}