2024 Day 11 Complete!

2024/day11/input

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+1750884 193 866395 7 1158 31 35216 0

2024/day11/main.go

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+package main
+
+import (
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	inp := h.StdinToString()
+	mc := part1(parseStones(inp))
+	part2(parseStones(inp), mc)
+}
+
+func part1(inp []int) *MemoCache {
+	mc := NewMemo()
+	fmt.Println("# Part 1")
+	fmt.Println("Stones After 25 Blinks:", mc.StonesAfter(inp, 25))
+	return mc
+}
+
+func part2(inp []int, mc *MemoCache) {
+	fmt.Println("# Part 2")
+	fmt.Println("Stones After 75 Blinks:", mc.StonesAfter(inp, 75))
+}
+
+func blink(stone int) []int {
+	var ret []int
+	if stone == 0 {
+		ret = append(ret, 1)
+	} else if evenDigits(stone) {
+		ret = append(ret, split(stone)...)
+	} else {
+		ret = append(ret, stone*2024)
+	}
+	return ret
+}
+
+// Attempt 1, I tracked the actual stones, but that's too much.
+// Attempt 2, Switch from tracking the actual stones to just the length
+type MemoKey struct {
+	stone  int
+	blinks int
+}
+type MemoCache struct {
+	cache map[MemoKey]int
+}
+
+func NewMemo() *MemoCache {
+	return &MemoCache{cache: make(map[MemoKey]int)}
+}
+
+func (mc *MemoCache) StonesAfter(stones []int, b int) int {
+	var res int
+	for _, s := range stones {
+		res += mc.SizeAfterBlinks(s, b)
+	}
+	return res
+}
+
+func (mc *MemoCache) SizeAfterBlinks(s, b int) int {
+	key := MemoKey{stone: s, blinks: b}
+	if v, ok := mc.cache[key]; ok {
+		return v
+	}
+	res := blink(s)
+	if b == 1 {
+		mc.cache[key] = len(res)
+		return len(res)
+	}
+	n := mc.SizeAfterBlinks(res[0], b-1)
+	if len(res) == 2 {
+		n += mc.SizeAfterBlinks(res[1], b-1)
+	}
+	mc.cache[key] = n
+	return n
+}
+
+func countDigits(i int) int {
+	if i == 0 {
+		return 0
+	}
+	return int(math.Floor(math.Log10(float64(i))) + 1)
+}
+
+func evenDigits(i int) bool {
+	return countDigits(i)%2 == 0
+}
+
+func split(i int) []int {
+	cnt := countDigits(i)
+	splitAt := cnt / 2
+	return []int{int(float64(i) / math.Pow10(splitAt)), i % int(math.Pow10(splitAt))}
+}
+
+func parseStones(inp string) []int {
+	var ret []int
+	pts := strings.Split(inp, " ")
+	for i := range pts {
+		w, _ := strconv.Atoi(pts[i])
+		ret = append(ret, w)
+	}
+	return ret
+}

2024/day11/testinput

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+0 1 10 99 999

2024/day11/testinput2

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+125 17