day7

day7/main.go

@@ -0,0 +1,106 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/kelindar/bitmap"
+)
+
+func readLines(filename string) []string {
+	raw, err := os.ReadFile(filename)
+	if err != nil {
+		panic(err)
+	}
+	return strings.Split(string(raw), "\n")
+}
+
+func main() {
+	filename := "input0.txt"
+	if len(os.Args) > 1 {
+		filename = os.Args[1]
+	}
+	lines := readLines(filename)
+	m := parseManifold(lines)
+	_, splits := m.eval()
+	fmt.Printf("%v\n", splits)
+	fmt.Printf("%v\n", m.quantumEval())
+}
+
+type manifold struct {
+	width     uint32
+	source    bitmap.Bitmap
+	splitters []bitmap.Bitmap
+}
+
+func (m *manifold) eval() (bitmap.Bitmap, uint64) {
+	splits := uint64(0)
+	active := m.source.Clone(nil)
+	for _, splitter := range m.splitters {
+		activated := active.Clone(nil)
+		activated.And(splitter)
+		var produced bitmap.Bitmap
+		activated.Range(func(i uint32) {
+			splits++
+			produced.Set(i - 1)
+			produced.Set(i + 1)
+		})
+		active.AndNot(activated)
+		active.Or(produced)
+	}
+	return active, splits
+}
+
+// set expansion is just too slow
+// instead, work like eval but use a slice of uints where the
+// values are the number of timelines that produce a tachyon
+// at a given position; when a tachyon is split and joins
+// an existing one, we increment, not just bitwise or.
+// the total is the sum of all timelines of all positions
+// in the final frame.
+// 3141808011 is too low
+func (m *manifold) quantumEval() uint64 {
+	active := make([]uint64, m.width)
+	m.source.Range(func(i uint32) {
+		active[i] = 1
+	})
+	for _, frame := range m.splitters {
+		next := make([]uint64, m.width)
+		copy(next, active)
+
+		for i, t := range active {
+			if t == 0 {
+				continue
+			}
+			splitter := frame.Contains(uint32(i))
+			if splitter {
+				next[i] = 0
+				next[i-1] += t
+				next[i+1] += t
+			}
+		}
+		active = next
+	}
+	total := uint64(0)
+	for _, x := range active {
+		total += x
+	}
+	return total
+}
+
+func parseManifold(lines []string) *manifold {
+	var m manifold
+	m.width = uint32(len(lines[0]))
+	m.source.Set(uint32(strings.Index(lines[0], "S")))
+	for i := 1; i < len(lines); i++ {
+		var splitter bitmap.Bitmap
+		for j, c := range lines[i] {
+			if c == '^' {
+				splitter.Set(uint32(j))
+			}
+		}
+		m.splitters = append(m.splitters, splitter)
+	}
+	return &m
+}