aoc day 14 part 2

day14part2.go

package main

import (
	"fmt"
	"math"
	"os"
	"strings"
)

func hash(id string) uint64 {
	return (uint64(id[0])-65)*26 + uint64(id[1]) - 65
}

func parseInput(data string, values []uint64) {
	for i := 1; i < len(data); i++ {
		values[hash(string(data[i-1])+string(data[i]))]++
	}
}

func iterate(values []uint64, conversions map[uint64]uint64) []uint64 {
	new_values := make([]uint64, 26*26)
	for i, n := range values {
		if _, ok := conversions[uint64(i)]; !ok || n == 0 {
			new_values[i] += n
			continue
		}
		new_values[uint64(i/26*26)+conversions[uint64(i)]] += n
		new_values[conversions[uint64(i)]*26+uint64(i%26)] += n
	}
	return new_values
}

func main() {
	dat, _ := os.ReadFile("day14.txt")
	split := strings.Split(string(dat), "\n")
	values := make([]uint64, 26*26)
	conversions := make(map[uint64]uint64, 0)

	parseInput(split[0], values)

	for i := 2; i < len(split); i++ {
		conversions[hash(strings.Split(split[i], " -> ")[0])] = hash("A" + strings.Split(split[i], " -> ")[1])
	}

	for i := 0; i < 40; i++ {
		values = iterate(values, conversions)
	}

	appearances := make([]uint64, 26)
	for i, n := range values {
		appearances[i/26] += n
		appearances[i%26] += n
	}
	appearances[hash("A"+string(string(dat)[0]))]++
	max := uint64(0)
	min := uint64(18446744073709551615)
	for i, n := range appearances {
		if n == 0 {
			continue
		}
		appearances[i] = uint64(math.Ceil(float64(n) / 2))
		if appearances[i] > max {
			max = appearances[i]
		}
		if appearances[i] < min {
			min = appearances[i]
		}
	}
	fmt.Println(max - min)
}