94 lines
1.9 KiB
Go
94 lines
1.9 KiB
Go
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package main
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import (
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"os"
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"fmt"
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"strconv"
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"strings"
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)
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// ---------------------------------------
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type Stone int64
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func (s Stone) blink() [2]Stone {
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stones := [...]Stone{-1, -1}
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num_str := strconv.Itoa(int(s))
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switch {
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// rule 1
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case s == 0:
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stones[0] = 1
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// rule 2
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case len(num_str) % 2 == 0:
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num1, err := strconv.Atoi(num_str[:len(num_str) / 2])
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check(err)
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num2, err := strconv.Atoi(num_str[len(num_str) / 2:])
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check(err)
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stones[0] = Stone(num1)
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stones[1] = Stone(num2)
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// rule 3
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default:
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stones[0] = s * 2024
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}
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return stones
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}
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// ---------------------------------------
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type Pair struct {
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s Stone
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n_steps uint32
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}
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var population_number_cache map[Pair]uint64
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func population_number(s Stone, n_steps uint32) uint64 {
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cache := population_number_cache[Pair{s, n_steps}]
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if cache != 0 { return cache }
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new_stones := s.blink()
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if n_steps == 0 { return 1 }
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p := population_number(new_stones[0], n_steps - 1)
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if new_stones[1] > -1 {
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p += population_number(new_stones[1], n_steps - 1)
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}
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population_number_cache[Pair{s, n_steps}] = p
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return p
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}
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func check(e error) { if e != nil { panic(e) } }
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func main() {
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// read in file
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dat, err := os.ReadFile("data.txt")
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check(err)
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dat_str := strings.TrimSpace(string(dat))
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line_arr := strings.Split(dat_str, " ")
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// convert to list of numbers
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stones := make([]Stone, 0, len(line_arr))
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for _, e := range line_arr {
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num, err := strconv.Atoi(e)
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check(err)
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stones = append(stones, Stone(num))
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}
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// init cache
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population_number_cache = make(map[Pair]uint64)
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// main calc
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len_acc := uint64(0)
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for _, stone := range stones {
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len_acc += population_number(stone, 75)
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}
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fmt.Println(len_acc)
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}
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