125 lines
2.3 KiB
Go
125 lines
2.3 KiB
Go
package main
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import (
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"fmt"
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h "git.bullercodeworks.com/brian/adventofcode/helpers"
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)
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func main() {
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inp := h.StdinToStringSlice()
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part1(inp)
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fmt.Println()
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part2(inp)
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}
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var (
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N = h.Coordinate{X: 0, Y: -1}
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E = h.Coordinate{X: 1, Y: 0}
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S = h.Coordinate{X: 0, Y: 1}
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W = h.Coordinate{X: -1, Y: 0}
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)
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// movement describes how a beam moving in a direction should react
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// to a byte
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var movement = map[h.Coordinate]map[byte][]h.Coordinate{
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N: {
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'|': {N},
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'-': {W, E},
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'\\': {W},
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'/': {E},
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'.': {N},
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},
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E: {
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'|': {N, S},
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'-': {E},
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'\\': {S},
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'/': {N},
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'.': {E},
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},
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S: {
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'|': {S},
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'-': {W, E},
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'\\': {E},
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'/': {W},
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'.': {S},
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},
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W: {
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'|': {N, S},
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'-': {W},
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'\\': {N},
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'/': {S},
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'.': {W},
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},
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}
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var tileHistory map[h.Coordinate][]h.Coordinate
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func part1(input []string) {
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mm := h.StringSliceToCoordByteMap(input)
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tileHistory = make(map[h.Coordinate][]h.Coordinate)
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proc(&mm, E, h.Coordinate{X: 0, Y: 0})
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fmt.Println("# Part 1")
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fmt.Println(len(tileHistory))
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}
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func part2(input []string) {
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mm := h.StringSliceToCoordByteMap(input)
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maxTiles := h.MIN_INT
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// starts are a map of positions -> directions to test as a starting point
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starts := make(map[*h.Coordinate]h.Coordinate)
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for y := mm.TLY; y <= mm.BRY; y++ {
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for x := mm.TLX; x <= mm.BRX; x++ {
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if y != mm.TLY && x != mm.TLX && y != mm.BRY && x != mm.BRX {
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continue
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}
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if y == mm.TLY {
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// South facing beams
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starts[&h.Coordinate{Y: y, X: x}] = S
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} else if y == mm.BRY {
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// North facing beams
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starts[&h.Coordinate{Y: y, X: x}] = N
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}
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if x == mm.TLX {
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// East facing beams
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starts[&h.Coordinate{Y: y, X: x}] = E
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}
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if x == mm.BRX {
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// West facing beams
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starts[&h.Coordinate{Y: y, X: x}] = W
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}
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}
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}
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for pos, dir := range starts {
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tileHistory = make(map[h.Coordinate][]h.Coordinate)
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proc(&mm, dir, *pos)
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if len(tileHistory) > maxTiles {
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maxTiles = len(tileHistory)
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}
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}
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fmt.Println("# Part 2")
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fmt.Println(maxTiles)
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}
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func proc(mm *h.CoordByteMap, dir, pos h.Coordinate) {
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if !mm.ContainsCoord(pos) {
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return
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}
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if visits, ok := tileHistory[pos]; ok {
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for _, v := range visits {
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if v == dir {
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return
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}
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}
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}
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curr := mm.Get(pos)
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tileHistory[pos] = append(tileHistory[pos], dir)
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next := movement[dir][curr]
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for _, n := range next {
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proc(mm, n, pos.Add(n))
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}
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}
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