h = Hash.new do |hash, key|
 hash.key = 'hi'
end
 
h['xxxx']  # => 'hi'
h['anything'] # => 'hi'

tri = Hash.new do |hash, key|
  col,row = key[0],key[1]
  if col == 1 || col == row
    hash[key] = 1
  elsif col > row
    hash[key] = 0
  else
    hash[key] = hash[[col, row-1]] + hash[[col-1, row-1]]
  end
end

for i in 1..10
  for j in 1..10
    print "#{tri[[j,i]]} "
  end
  puts ""
end