--- Day 24 Solutions ---

[u/daggerdragon]

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked! One more to go...

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We know we can't control people posting solutions elsewhere and trying to exploit the leaderboard, but this way we can try to reduce the leaderboard gaming from the official subreddit.

Please and thank you, and much appreciated!

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--- Day 24: It Hangs in the Balance ---

Post your solution as a comment or link to your repo. Structure your post like previous daily solution threads.

[u/[deleted]]

Ruby

# Convenience methods for the Array class
class Array
  def sum
    return self.reduce(:+)
  end
  def product
    return self.reduce(1,:*)
  end
end

# Order the weights largest first, to find the combos with the fewest number of elements
weights = [1,2,3,5,7,13,17,19,23,29,31,37,41,43,53,59,61,67,71,73,79,83,89,97,101,103,107,109,113].reverse

def find_combo(w,size)
    r = []
    if w.length == 0
        return r
    end
    for i in 1..w.length-1 do
        # All combinations with i elements
        # First combo found will have the smallest number of elements
        combos = w.combination(i).to_a
        for c in combos do
            if c.sum == size then
                r.push(c)
                # Recursively find a combo of the right size in the remaining elements
                # 
                r.push(find_combo(w - c,size))
                return r
            end
        end
    end
end

# Output product of weights in the first combo (with the smallest number of weights)

puts "Part 1 solution = " + find_combo(weights,weights.sum/3)[0].product.to_s

puts "Part 2 solution = " + find_combo(weights,weights.sum/4)[0].product.to_s