Generates all possible football goal sequences leading to a score of 21

football.rb

def football(results, trace, sum, roots, nodes)
  results_p = results.dup
  if sum < 0
    return results_p
  elsif sum == 0
    return results_p << trace
  else
    nodes_p = nodes.dup
    roots.each {|rt| nodes_p << rt } # push each root on the node stack
    while r = nodes_p.pop
      results_p = results_p + football(results, trace + [r], sum - r, roots, nodes_p)
    end
    results_p
  end
end

football([], [], 21, [2, 3, 7], []).each {|trace| p [trace, trace.inject(0, :+)]}

# --SNIP--
# [[2, 2, 2, 2, 2, 2, 2, 7], 21]
# [[2, 2, 2, 2, 2, 2, 2, 3, 2, 2], 21]
# [[2, 2, 2, 2, 2, 2, 2, 3, 2, 2], 21]
# [[2, 2, 2, 2, 2, 2, 2, 3, 2, 2], 21]
# [[2, 2, 2, 2, 2, 2, 2, 2, 3, 2], 21]
# [[2, 2, 2, 2, 2, 2, 2, 2, 3, 2], 21]
# [[2, 2, 2, 2, 2, 2, 2, 2, 2, 3], 21]
# 6219