Day 5: Print Queue

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FAQ

  • reboot6675
    1·
    10 days ago

    Go

    Using a map to store u|v relations. Part 2 sorting with a custom compare function worked very nicely

    spoiler 
    func main() {
	file, _ := os.Open("input.txt")
	defer file.Close()
	scanner := bufio.NewScanner(file)

	mapPages := make(map[string][]string)
	rulesSection := true
	middleSumOk := 0
	middleSumNotOk := 0

	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			rulesSection = false
			continue
		}

		if rulesSection {
			parts := strings.Split(line, "|")
			u, v := parts[0], parts[1]
			mapPages[u] = append(mapPages[u], v)
		} else {
			update := strings.Split(line, ",")
			isOk := true

			for i := 1; i < len(update); i++ {
				u, v := update[i-1], update[i]
				if !slices.Contains(mapPages[u], v) {
					isOk = false
					break
				}
			}

			middlePos := len(update) / 2
			if isOk {
				middlePage, _ := strconv.Atoi(update[middlePos])
				middleSumOk += middlePage
			} else {
				slices.SortFunc(update, func(u, v string) int {
					if slices.Contains(mapPages[u], v) {
						return -1
					} else if slices.Contains(mapPages[v], u) {
						return 1
					}
					return 0
				})
				middlePage, _ := strconv.Atoi(update[middlePos])
				middleSumNotOk += middlePage
			}
		}
	}

	fmt.Println("Part 1:", middleSumOk)
	fmt.Println("Part 2:", middleSumNotOk)
}
    • HeckGazer@programming.dev
      1·
      9 days ago

      Because you’re just sorting integers and in a single pass, the a == b and a > b distinction doesn’t actually matter here, so the cmp can very simply be is a|b in rules, no map needed.

      Edit: I realise it would be a sidegrade for your case because of how you did P1, just thought it was an interesting insight, especially for those that did P1 by checking if the input was sorted using the same custom compare.

      func solution(input string) (int, int) {
	// rules: ["a|b", ...]
	// updates: [[1, 2, 3, 4], ...]
	var rules, updates = parse(input)

	sortFunc := func(a int, b int) int {
		if slices.Contains(rules, strconv.Itoa(a)+"|"+strconv.Itoa(b)) {
			return -1
		}
		return 1
	}

	var sumOrdered = 0
	var sumUnordered = 0
	for _, update := range updates {
		if slices.IsSortedFunc(update, sortFunc) {
			sumOrdered += update[len(update)/2]
		} else {
			slices.SortStableFunc(update, sortFunc)
			sumUnordered += update[len(update)/2]
		}
	}
	return sumOrdered, sumUnordered
}