Challenge from a friend: "Design a function that selects the top k from n items using a reduce." This is my naive 5-min solution.

doit.rb

def doit(k, array)
  array.reduce([]) do |memo,o|
    if memo.length < k
      memo << o
    elsif (min = memo.min) < o
      memo[memo.index(min)] = o
    end
      memo
  end
end

array = [1,3,5,7,9,2,4,6,8,10]
doit(3, array) #=> [10, 9, 8]
doit(4, array) #=> [9, 10, 8, 7]