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