advent-of-code-2024/day11/stones.go

package main

import (
    "os"
    "fmt"
    "strconv"
    "strings"
)


// general util
func check(e error) {
    if e != nil { panic(e) }
}

func apply_rules(arr []int) []int {
    for i, e := range arr {
        switch {
            // rule 1
            case e == 0:
                arr[i] = 1
            // mark for rule 2
            case len(strconv.Itoa(e)) % 2 == 0:
                arr[i] = -e
            // rule 3
            default:
                arr[i] = e * 2024
        }
    }
    // rule 2
    arr_cp := make([]int, len(arr))
    copy(arr_cp, arr)
    arr = arr[:0]

    for _, e := range arr_cp {
        if e > 0 {
            arr = append(arr, e)
        } else {
            e_str := strconv.Itoa(-e)
            num1, err := strconv.Atoi(e_str[:len(e_str) / 2])
            check(err)
            num2, err := strconv.Atoi(e_str[len(e_str) / 2:])
            check(err)
            
            arr = append(arr, num1)
            arr = append(arr, num2)
        }
    }

    return arr
}


// main loop
func main() {

    // read in file
    dat, err := os.ReadFile("data.txt")
    check(err)
    dat_str := strings.TrimSpace(string(dat))
    line_arr := strings.Split(dat_str, " ")

    // convert to list of numbers
    numbers := make([]int, 0, len(line_arr))

    for _, e := range line_arr {
        num, err := strconv.Atoi(e)
        check(err)
        numbers = append(numbers, num)
    }

    for range 25 {
        numbers = apply_rules(numbers)
    }
    fmt.Println(len(numbers))
}