advent-of-code-2023/day-15/part2.go

64 lines
1.3 KiB
Go

package main
import (
"slices"
"strconv"
"strings"
)
type lens struct {
focal_length int
label string
}
func part2(input string) int {
instructions := strings.Split(input, ",")
boxes := make([][]lens, 256)
for _, instruction := range instructions {
if strings.Contains(instruction, "=") {
split := strings.Split(instruction, "=")
label := split[0]
box_index := hash(label)
focal_length, _ := strconv.Atoi(split[1])
found_box := boxes[box_index]
lens_index := slices.IndexFunc(found_box, func(l lens) bool {
return l.label == label
})
if lens_index >= 0 {
found_box[lens_index] = lens{focal_length, label}
boxes[box_index] = found_box
} else {
boxes[box_index] = append(found_box, lens{focal_length, label})
}
} else if strings.Contains(instruction, "-") {
split := strings.Split(instruction, "-")
label := split[0]
box_index := hash(label)
found_box := boxes[box_index]
boxes[box_index] = slices.DeleteFunc(found_box, func(l lens) bool {
return l.label == label
})
}
}
sum := 0
for box_number, box := range boxes {
for slot_number, lens := range box {
sum += ((box_number + 1) * (slot_number + 1) * lens.focal_length)
}
}
return sum
}
func hash(input string) int {
sum := 0
for _, c := range input {
sum += int(c)
sum *= 17
sum %= 256
}
return sum
}