AoC23/d15.go

package main

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

type input []string

func parse(f string) (seq input) {
    seq = make(input, 0)

    for _, step := range strings.Split(f, ",") {
        step = strings.TrimSpace(step)
        seq = append(seq, step)
    }

    return
}

func hash(in string) (hash uint8) {
    hash = 0
    for _, byt := range []byte(in) {
        hash += byt
        hash *= 17
    }
    return
}

func part1(seq input) (sum uint) {
    for _, step := range seq { sum += uint(hash(step)) }
    return
}

type lens struct {
    label string
    focal uint64
}

func lens_find_label(arr []lens, label string) (pos int) {
    for pos, val := range arr{
        if val.label == label { return pos }
    }
    return -1
}

func part2(seq input) (sum uint64) {
    boxes := [256][]lens{}
    for i := 0; i < 256; i++ { boxes[i] = make([]lens, 0) }

    for _, step := range seq {
        var label string
        var op byte

        var off int
        if strings.Index(step, "=") >= 0 {
            off = strings.Index(step, "=")
            label = step[:off]
            op = step[off]
        } else if strings.Index(step, "-") >= 0 {
            off = strings.Index(step, "-")
            label = step[:off]
            op = step[off]
        }

        box := &boxes[hash(label)]
        pos := lens_find_label(*box, label)

        switch op {
        case '=':
            focal, _ := strconv.ParseUint(step[off + 1:], 0, 64)
            newlens := lens{
                label: label,
                focal: focal,
            }
            if pos >= 0 {
                (*box)[pos] = newlens
            } else {
                *box = append(*box, newlens)
            }

        case '-':
            if pos >= 0 {
                *box = append((*box)[:pos], (*box)[pos + 1:]...)
            }
        }
    }

    sum = 0
    for box_i, box := range boxes {
        for lens_i, lens := range box {
            fmt.Println(box_i + 1, ":", lens_i + 1, lens.label, lens.focal)
            sum += uint64(1 + box_i) * uint64(1 + lens_i) * lens.focal
        }
    }

    return
}

func main() {
    file, _ := os.ReadFile(os.Args[1])
    f := string(file)

    in := parse(f)
    fmt.Println(part1(in))
    fmt.Println(part2(in))
}