Day 12: Christmas Tree Farm

There are some presents to be given to young Elves and we need to find if they fit in given regions. The situation looks like this:

(def example "0:
###
##.
##.

1:
###
##.
.##

2:
.##
###
##.

3:
##.
###
##.

4:
###
#..
###

5:
###
.#.
###

4x4: 0 0 0 0 2 0
12x5: 1 0 1 0 2 2
12x5: 1 0 1 0 3 2")

…and the way the real input is created we can ignore all but the last paragraph, which tells us the size of a region and an amount of each present that we should try to fit in that region.

Input parsing

To split the input into paragraphs, we have the aoc/parse-paragraphs function ready.
We will extract integers from the last paragraph.

(defn parse-data [input]
  (last (aoc/parse-paragraphs input :ints)))

(def example-data (parse-data example))

(def data (parse-data (aoc/read-input 12)))

example-data

[[4 4 0 0 0 0 2 0] [12 5 1 0 1 0 2 2] [12 5 1 0 1 0 3 2]]

Solution

The solution which works for the real input is very simple. Maybe even too simple.
Every present has a 3x3 shape, i.e. its area is 9. We won’t try anything fancy and we’ll just check if we can fit every present in its own 3x3 area.

Each line of the parsed input contains multiple integers. The first two are the width and the height of a region, and the rest are the amounts of each present.
The presents fit if their total area is not larger than the area of a region.

(defn fits? [[w h & amounts]]
  (<= (* 9 (reduce + amounts)) (* w h)))

And to solve the task, we just count those lines that satisfy the above condition.

(defn solve [measures]
  (aoc/count-if fits? measures))

(solve data)

575

That’s it.

That’s it?!

Conclusion

I usually like easy tasks. But this one wasn’t easy, it was lame.
What a disappointing way to end what was an interesting AoC year.

No highlights today.

source: clojure/src/day12.clj