Prints all possible scores in a bouldering contest, given the number of problems and points system

boulder_scores.rb

PROBLEMS = 20
SCORES = [10, 7, 4, 1, 0]
def permutations_of_scores
  result = [ [0]*(SCORES.length-1) + [PROBLEMS] ]
  while( result.last != [PROBLEMS] + [0]*(SCORES.length-1) )
    result << next_permutation(result.last.dup)
  end
  result
end

def next_permutation(perm)
  # Take 1 from last non-zero
  # Increment one to the left
  # If furthest right was == 0, then move all but leftmost into it
  need_to_shift_digits = perm[-1].zero?
  last_nonzero_index = ->(p){p.size - 1 - p.reverse.find_index{|x| x > 0}} 
  incremented_index = last_nonzero_index.call(perm) - 1
  perm[incremented_index+1] -= 1 # From last nonzero element
  perm[incremented_index] += 1 # To the left, to the left
  if need_to_shift_digits
    (perm[last_nonzero_index.call(perm[0..-2])] -= 1; perm[-1] += 1) while last_nonzero_index.call(perm[0..-2]) != incremented_index
  end
  perm
end

# Table header
puts "#{SCORES.join(", ")} Total"
# Table results
permutations_of_scores.each { |p| puts "#{p.join(", ")}, #{p.each_with_index.map {|n, i| n*SCORES[i]}.inject(:+)}" }