Fibonacci Number code challenge

The Fibonacci Number is another common code challenge and it has some simililraties with the Factorial Number we already solved.

In this videos I show three ways to implement a solution for this problem following similar approaches: iterative loop, recursion and using inject (which is also iterative, but it’s cooler).

1. Iterative (upto loop):

   def fibo(n)
     seq = [0, 1]
     2.upto(n).each do |i|
    seq[i] = seq[i-1] + seq[i-2]
     end
     seq[n]
   end
   

2. Recursive:

   def fibo(n)
     return n if n <= 1
     fibo(n-1) + fibo(n-2)  
   end
   

3. Using inject:

   def fibo(n)
     return n if n <= 1
     (2..n).inject([0,1]){|fib| fib << fib[-1] + fib[-2]}[n]
   end