Fibonacci sequence in Ruby (recursion)

Question

I\'m trying to implement the following function, but it keeps giving me the stack level too deep (SystemStackError) error.

Any ideas what the problem mi

Answer 1

This is not the way you calculate fibonacci, you are creating huge recursive tree which will fail for relatively small ns. I suggest you do something like this:

def fib_r(a, b, n)
  n == 0 ? a : fib_r(b, a + b, n - 1)
end

def fib(n)
  fib_r(0, 1, n)
end

p (0..100).map{ |n| fib(n) }

Answer 2

Here is a more concise solution that builds a lookup table:

fibonacci = Hash.new do |hash, key|
  if key <= 1
    hash[key] = key
  else
    hash[key] = hash[key - 1] + hash[key - 2]
  end
end

fibonacci[10]
# => 55 
fibonacci
# => {1=>1, 0=>0, 2=>1, 3=>2, 4=>3, 5=>5, 6=>8, 7=>13, 8=>21, 9=>34, 10=>55}

Answer 3

Try this oneliner

def fib (n)
    n == 0 || n == 1 ? n : fib(n-2) + fib(n-1)
end
print fib(16)

Output: 987

Answer 4

We can perform list fibo series using below algorithm

def fibo(n)
  n <= 2 ? 1 : fibo(n-1) + fibo(n-2)
end

We can generate series like below

p (1..10).map{|x| fibo(x)}

below is the output of this

=> [1, 1, 2, 3, 5, 8, 13, 21, 34, 55] 

Answer 5

fastest and smallest in lines solution:

fiby = ->(n, prev, i, count, selfy) {
  i < count ? (selfy.call n + prev, n, i + 1, count, selfy) : (puts n)
}
fiby.call 0, 1, 0, 1000, fiby

functional selfie pattern :)

Answer 6

Joining the Fibonacci train:

Regular:

def fib(num)
  return num if (num < 2) else fib(num-1) + fib(num-2)
end

With caching:

module Fib
  @fibs = [0,1]
  def self.calc(num)
    return num if (num < 2) else @fibs[num] ||= self.calc(num-1) + self.calc(num-2)
  end
end