aoc_2024/2025/five/five.go

package main

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

type freshRange struct {
	start, end int
}

type freshDB struct {
	ranges []freshRange
}

func (r *freshRange) contains(c int) bool {
	return c >= r.start && c <= r.end
}

func (r *freshRange) nInRange() int {
	total := (r.end - r.start) + 1
	return total
}

/* Check for an error, panic if there is */
func check(err error) {
	if err != nil {
		panic(err)
	}
}

func dbFromSlice(ranges []int) (db freshDB, err error) {
	if len(ranges)%2 != 0 {
		return freshDB{}, errors.New("Input slice not of even length")
	}

	db.ranges = make([]freshRange, 0, len(ranges)/2)

	for i := 0; i < len(ranges); i += 2 {
		db.ranges = append(db.ranges, freshRange{ranges[i], ranges[i+1]})
	}
	return db, nil
}

/* Parse ranges out of a bufio.Scanner */
func parse(scanner *bufio.Scanner) (db freshDB, err error) {
	db.ranges = make([]freshRange, 0, 5)

	for scanner.Scan() {
		text := scanner.Text()

		if text == "" {
			return db, nil
		}

		startEnd := strings.Split(text, "-")

		if len(startEnd) != 2 {
			return db, errors.New("Fresh range does not contain exactly two numbers")
		}

		start, err := strconv.Atoi(startEnd[0])
		if err != nil {
			return db, err
		}

		end, err := strconv.Atoi(startEnd[1])
		if err != nil {
			return db, err
		}

		db.ranges = append(db.ranges, freshRange{start, end})
	}
	return db, errors.New("No empty line in file to delimit fresh ranges")
}

func (db *freshDB) insert(toinsert freshRange) {
	for i := range db.ranges {
		r := &db.ranges[i]
		if r.contains(toinsert.start) {
			if toinsert.end > r.end {
				r.end = toinsert.end
			}
			return
		}

		if r.contains(toinsert.end) {
			if toinsert.start < r.start {
				r.start = toinsert.start
			}
			return
		}

		if toinsert.contains(r.start) && toinsert.contains(r.end) {
			r.start = toinsert.start
			r.end = toinsert.end
			return
		}
	}
	db.ranges = append(db.ranges, toinsert)
}

/* Collapse a list of fresh ingredient ranges to avoid overlaps */
func (db *freshDB) collapse() (before int, after int) {
	before = len(db.ranges)
	collapsed := freshDB{make([]freshRange, 0, len(db.ranges))}

	for _, r := range db.ranges {
		collapsed.insert(r)
	}
	db.ranges = collapsed.ranges
	after = len(db.ranges)
	return before, after
}

func main() {

	file, err := os.Open("five.txt")
	check(err)
	defer file.Close()

	scanner := bufio.NewScanner(file)
	db, err := parse(scanner)
	check(err)

	nRaw := len(db.ranges)

	for {
		before, after := db.collapse()

		fmt.Printf("Collapsed %d to %d ranges\n", before, after)

		if before == after {
			break
		}
	}

	potentialNFresh := 0
	for _, r := range db.ranges {
		potentialNFresh += r.nInRange()
	}

	fmt.Printf(
		"N raw %d and consolidated %d. %d potential fresh ingredients.\n",
		nRaw,
		len(db.ranges),
		potentialNFresh,
	)
}