Day 06 - 2019

day-06.go

package main

import (
	"io"
	"log"

	"github.com/bozdoz/advent-of-code-2025/utils"
)

type d = []string

func partOne(data d) (ans any) {
	orbits := newOrbits(data)

	count := 0

	for _, v := range orbits.depth {
		count += v
	}

	return count
}

func partTwo(data d) (ans any) {
	seen := map[string]bool{}

	orbits := newOrbits(data)

	cur := "YOU"
	for cur != "COM" {
		next := orbits.objects[cur]

		seen[next] = true

		cur = next
	}

	// find orbit in common

	cur = "SAN"

	for !seen[cur] {
		cur = orbits.objects[cur]
	}

	common := orbits.depth[cur]

	// diff of YOU vs common
	// diff of SAN vs common
	// minus 2 because YOU and SAN don't count
	transfers := orbits.depth["YOU"] - common + orbits.depth["SAN"] - common - 2

	return transfers
}

func init() {
	log.SetOutput(io.Discard)
}

var day = utils.NewDay[d]()

func main() {
	day.Read("./input.txt")

	day.Run(partOne)
	day.Run(partTwo)
}

orbits.go

package main

import (
	"strings"
)

type Orbits struct {
	objects map[string]string
	// distance from center
	depth map[string]int
}

func newOrbits(data d) *Orbits {
	orbits := Orbits{
		objects: map[string]string{},
		depth:   map[string]int{},
	}

	for _, val := range data {
		arr := strings.Split(val, ")")

		orbits.objects[arr[1]] = arr[0]
	}

	for k, v := range orbits.objects {
		if v == "COM" {
			orbits.depth[k] = 1
		} else {
			// iterate orbits until we get COM
			deps := []string{k, v}
			// get next
			for {
				k = v
				v = orbits.objects[k]
				if v == "COM" {
					// first time getting to the core
					// imagine c:b b:COM
					for i := range deps {
						orbits.depth[deps[i]] = len(deps) - i
					}

					break
				}
				if orbits.depth[v] > 0 {
					// imagine d:c c:b
					established := orbits.depth[v]
					for i := range deps {
						orbits.depth[deps[i]] = established + len(deps) - i
					}
					break
				}

				// keep going
				deps = append(deps, v)
			}
		}
	}

	return &orbits
}