2023 Day 16 Complete!

2023-12-16 10:17:04 -06:00
parent 5769c7e75c
commit a34f05d1af
4 changed files with 447 additions and 0 deletions
--- a/2023/day16/main.go
+++ b/2023/day16/main.go
@@ -0,0 +1,124 @@
+package main
+
+import (
+	"fmt"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	inp := h.StdinToStringSlice()
+	part1(inp)
+	fmt.Println()
+	part2(inp)
+}
+
+var (
+	N = h.Coordinate{X: 0, Y: -1}
+	E = h.Coordinate{X: 1, Y: 0}
+	S = h.Coordinate{X: 0, Y: 1}
+	W = h.Coordinate{X: -1, Y: 0}
+)
+
+// movement describes how a beam moving in a direction should react
+// to a byte
+var movement = map[h.Coordinate]map[byte][]h.Coordinate{
+	N: {
+		'|':  {N},
+		'-':  {W, E},
+		'\\': {W},
+		'/':  {E},
+		'.':  {N},
+	},
+	E: {
+		'|':  {N, S},
+		'-':  {E},
+		'\\': {S},
+		'/':  {N},
+		'.':  {E},
+	},
+	S: {
+		'|':  {S},
+		'-':  {W, E},
+		'\\': {E},
+		'/':  {W},
+		'.':  {S},
+	},
+	W: {
+		'|':  {N, S},
+		'-':  {W},
+		'\\': {N},
+		'/':  {S},
+		'.':  {W},
+	},
+}
+
+var tileHistory map[h.Coordinate][]h.Coordinate
+
+func part1(input []string) {
+	mm := h.StringSliceToCoordByteMap(input)
+	tileHistory = make(map[h.Coordinate][]h.Coordinate)
+	proc(&mm, E, h.Coordinate{X: 0, Y: 0})
+
+	fmt.Println("# Part 1")
+	fmt.Println(len(tileHistory))
+}
+
+func part2(input []string) {
+	mm := h.StringSliceToCoordByteMap(input)
+
+	maxTiles := h.MIN_INT
+	// starts are a map of positions -> directions to test as a starting point
+	starts := make(map[*h.Coordinate]h.Coordinate)
+	for y := mm.TLY; y <= mm.BRY; y++ {
+		for x := mm.TLX; x <= mm.BRX; x++ {
+			if y != mm.TLY && x != mm.TLX && y != mm.BRY && x != mm.BRX {
+				continue
+			}
+			if y == mm.TLY {
+				// South facing beams
+				starts[&h.Coordinate{Y: y, X: x}] = S
+			} else if y == mm.BRY {
+				// North facing beams
+				starts[&h.Coordinate{Y: y, X: x}] = N
+			}
+			if x == mm.TLX {
+				// East facing beams
+				starts[&h.Coordinate{Y: y, X: x}] = E
+			}
+			if x == mm.BRX {
+				// West facing beams
+				starts[&h.Coordinate{Y: y, X: x}] = W
+			}
+		}
+	}
+	for pos, dir := range starts {
+		tileHistory = make(map[h.Coordinate][]h.Coordinate)
+		proc(&mm, dir, *pos)
+		if len(tileHistory) > maxTiles {
+			maxTiles = len(tileHistory)
+		}
+	}
+
+	fmt.Println("# Part 2")
+	fmt.Println(maxTiles)
+}
+
+func proc(mm *h.CoordByteMap, dir, pos h.Coordinate) {
+	if !mm.ContainsCoord(pos) {
+		return
+	}
+	if visits, ok := tileHistory[pos]; ok {
+		for _, v := range visits {
+			if v == dir {
+				return
+			}
+		}
+	}
+	curr := mm.Get(pos)
+	tileHistory[pos] = append(tileHistory[pos], dir)
+	next := movement[dir][curr]
+	for _, n := range next {
+		proc(mm, n, pos.Add(n))
+	}
+}