fib_up_to.rb

# List all values in fibonacci series <= n
def fib_up_to(n)
  return [] if n < 0 # Idiot-proofing.

  vals, succ = [0], 1

  while succ <= n
    vals << succ
    succ = vals[-1] + vals[-2]
  end

  vals
end

(-1..25).each do |i|
  puts "#{i}: #{fib_up_to i}"
end

=begin
-1: []
0: [0]
1: [0, 1, 1]
2: [0, 1, 1, 2]
3: [0, 1, 1, 2, 3]
4: [0, 1, 1, 2, 3]
5: [0, 1, 1, 2, 3, 5]
6: [0, 1, 1, 2, 3, 5]
7: [0, 1, 1, 2, 3, 5]
8: [0, 1, 1, 2, 3, 5, 8]
9: [0, 1, 1, 2, 3, 5, 8]
10: [0, 1, 1, 2, 3, 5, 8]
11: [0, 1, 1, 2, 3, 5, 8]
12: [0, 1, 1, 2, 3, 5, 8]
13: [0, 1, 1, 2, 3, 5, 8, 13]
14: [0, 1, 1, 2, 3, 5, 8, 13]
15: [0, 1, 1, 2, 3, 5, 8, 13]
16: [0, 1, 1, 2, 3, 5, 8, 13]
17: [0, 1, 1, 2, 3, 5, 8, 13]
18: [0, 1, 1, 2, 3, 5, 8, 13]
19: [0, 1, 1, 2, 3, 5, 8, 13]
20: [0, 1, 1, 2, 3, 5, 8, 13]
21: [0, 1, 1, 2, 3, 5, 8, 13, 21]
22: [0, 1, 1, 2, 3, 5, 8, 13, 21]
23: [0, 1, 1, 2, 3, 5, 8, 13, 21]
24: [0, 1, 1, 2, 3, 5, 8, 13, 21]
=end