day 11

11/eleven.go

@@ -0,0 +1,69 @@
+package eleven
+
+import (
+	"strconv"
+	"strings"
+
+	"github.com/cdlewis/advent-of-code/util"
+	"github.com/cdlewis/advent-of-code/util/aoc"
+	"github.com/cdlewis/advent-of-code/util/cast"
+)
+
+var cache = map[[3]int]int{}
+
+func Eleven() int {
+	stones := util.Map(strings.Split(aoc.GetInput(11, false, "125 17"), " "), cast.ToInt)
+	return simulate(stones, 75)
+}
+
+func simulate(stones []int, steps int) int {
+	result := 0
+
+	if len(stones) == 2 {
+		key := [3]int{stones[0], stones[1], steps}
+		if val, ok := cache[key]; ok {
+			return val
+		}
+		defer func() {
+			cache[key] = result
+		}()
+	}
+
+	for currentStep := range steps {
+		for idx, s := range stones {
+			if s == -1 {
+				continue
+			}
+
+			if s == 0 {
+				stones[idx] = 1
+				continue
+			}
+
+			digits := strconv.Itoa(s)
+			if len(digits)%2 == 0 {
+				stones[idx] = -1
+
+				simResult := simulate(
+					[]int{
+						cast.ToInt(digits[:len(digits)/2]),
+						cast.ToInt(digits[len(digits)/2:]),
+					},
+					steps-currentStep-1,
+				)
+
+				result += simResult
+				continue
+			}
+
+			stones[idx] *= 2024
+		}
+	}
+
+	for _, s := range stones {
+		if s != -1 {
+			result++
+		}
+	}
+	return result
+}

11/eleven_test.go

@@ -0,0 +1,9 @@
+package eleven
+
+import "testing"
+
+func TestEleven(t *testing.T) {
+	if Eleven() != 220357186726677 {
+		t.Error("unexpected result")
+	}
+}

11/input_11

@@ -0,0 +1 @@
+6563348 67 395 0 6 4425 89567 739318

util/list.go

@@ -10,7 +10,7 @@ func (l *List) Append(i int) {
 		l.Head = &Node{Val: i}
 		l.Tail = l.Head
 	} else {
-		l.Tail = l.Tail.Append(i)
+		l.Tail = l.Tail.InsertAfter(i)
 	}
 }
 
@@ -103,7 +103,7 @@ func (n *Node) ToSlice() []int {
 	return results
 }
 
-func (n *Node) Append(i int) *Node {
+func (n *Node) InsertAfter(i int) *Node {
 	next := &Node{Val: i}
 	next.Prev = n
 	n.Next = next