adventofcode/2024/day22/main.go

package main

import (
	"fmt"

	h "git.bullercodeworks.com/brian/adventofcode/helpers"
)

func main() {
	inp := h.StdinToIntSlice()
	part1(inp)
	fmt.Println()
	part2(inp)
}

func part1(inp []int) {
	var total int
	for i := range inp {
		total += steps(inp[i], 2000)
	}
	fmt.Println("# Part 1")
	fmt.Println(total)
}

var cache map[int]map[string]int

func part2(inp []int) {
	fmt.Println("# Part 2")
	cache = make(map[int]map[string]int)
	for i := range inp {
		wrk := inp[i]
		cache[inp[i]] = make(map[string]int)
		s := Seq{}
		for n := 0; n < 2000; n++ {
			next := step(wrk)
			seqChg := (next % 10) - (wrk % 10)
			s.Add(seqChg)
			if s.Len() == 4 {
				if _, ok := cache[inp[i]][s.String()]; !ok {
					cache[inp[i]][s.String()] = worth(next)
				}
			}
			wrk = next
		}
	}
	var best int
	var bestKey string
	checkedKeys := make(map[string]bool)
	for i := range inp {
		if i > 0 {
			h.ClearProgress()
		}
		h.PrintProgress(i, len(inp))
		for k := range cache[inp[i]] {
			if _, ok := checkedKeys[k]; ok {
				continue
			}
			var total int
			for j := range inp {
				total += cache[inp[j]][k]
			}
			if total > best {
				best = total
				bestKey = k
			}
			checkedKeys[k] = true
		}
	}
	fmt.Println()
	fmt.Println("Most Bananas:", best, bestKey)
}

const prune = 16777216

func steps(n, cnt int) int {
	for i := 0; i < cnt; i++ {
		n = step(n)
	}
	return n
}

func step(n int) int {
	n ^= (n * 64)
	n %= prune
	n ^= (n / 32)
	n %= prune
	n ^= (n * 2048)
	n %= prune
	return n
}

func worth(n int) int {
	return n % 10
}

type Seq struct {
	s []int
}

func (s *Seq) Len() int { return len(s.s) }

func (s *Seq) Add(n int) {
	if len(s.s) >= 4 {
		s.s = append(s.s[1:], n)
	} else {
		s.s = append(s.s, n)
	}
}

func (s Seq) String() string {
	var ret string
	for i := range s.s {
		ret = fmt.Sprintf("%s,%d", ret, s.s[i])
	}
	return ret[1:]
}