A linear time solution for the ArrayHopper problem.

array_hopper.rb

numbers = File.read(ARGV.first).split.map &:to_i

best_path = [0]

loop do
  current_pos = best_path.last
  max_hop = numbers[current_pos]
  candidates = (1..max_hop).map { |hop| current_pos + hop }
  if candidates.empty?
    best_path = ["failure"]
    break
  end
  if candidates.any? { |pos| pos >= numbers.length }
    best_path << "out"
    break
  end
  best_path << candidates.max_by { |pos| [numbers[pos] + pos, pos] }
end

puts best_path.join ", "