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package main
import (
"bufio"
"fmt"
"os"
"slices"
"strconv"
)
func main() {
fmt.Println(part1([]int64{1, 10, 100, 2024}), 37327623)
fmt.Println(part1(readData("data.txt")), 13004408787)
fmt.Println(part2([]int64{1, 2, 3, 2024}), 23)
fmt.Println(part2(readData("data.txt")))
}
func part1(init []int64) (result int64) {
for _, n := range init {
for range 2000 {
n = next(n)
}
result += n
}
return
}
func makeChangeId(memory [4]int, i int) (result int) {
for j := range 4 {
result = result*19 + memory[(i+j)%4] + 9
}
return
}
func part2(init []int64) int {
priceForChangeId := make([]int, 19*19*19*19)
for _, n := range init {
seenChange := make([]bool, 19*19*19*19)
prevPrice := n % 10
memory := [4]int{0, 0, 0, 0}
for i := range 2000 {
n2 := next(n)
price := n2 % 10
change := price - prevPrice
memory[i%4] = int(change)
if i >= 3 {
changeId := makeChangeId(memory, i)
if !seenChange[changeId] {
seenChange[changeId] = true
priceForChangeId[changeId] += int(price)
}
}
n, prevPrice = n2, price
}
}
return slices.Max(priceForChangeId)
}
func prune(a int64) int64 {
return a % 16777216
}
func next(a int64) int64 {
a = prune((a << 6) ^ a)
a = prune((a >> 5) ^ a)
a = prune((a << 11) ^ a)
return a
}
func readData(fileName string) (numbers []int64) {
fp, _ := os.Open(fileName)
scanner := bufio.NewScanner(fp)
for scanner.Scan() {
n, _ := strconv.ParseInt(scanner.Text(), 10, 64)
numbers = append(numbers, n)
}
return
}
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