Reverse an array without using a loop in ruby

Question

I have a coding challenge to reverse a an array with 5 elements in it. How would I do this without using the reverse method?

Code:

def reverse(array)
 a         


        

Answer 1

Recursion indeed is the solution if you're not going to use a loop. while or until is still a loop, and using built-in methods not doing recursion may also still be using a loop internally.

#!/usr/bin/env ruby

a = [1, 2, 3]

def reverse(array)
  t = array.pop
  reverse(array) if array.length > 0
  array.unshift t
end

puts reverse(Array.new(a)).inspect # [3, 2, 1]

Update

Naturally recursion has limits since it depends on the stack but that's the best you can have if you don't want to use a loop. Following Cary Swoveland's post, this is the benchmark on 8500 elements:

                         user     system      total        real
@Grych               0.060000   0.010000   0.070000 (  0.073179)
@ArupRakshit         0.000000   0.000000   0.000000 (  0.000836)
@konsolebox          0.000000   0.000000   0.000000 (  0.001771)
@JörgWMittag recursion  0.050000   0.000000   0.050000 (  0.053475)
@Jörg        tail    0.210000   0.040000   0.250000 (  0.246849)
@Jörg        fold    0.040000   0.010000   0.050000 (  0.045788)
@Jörg        loop    0.000000   0.000000   0.000000 (  0.000924)
Cary         rotate  0.060000   0.000000   0.060000 (  0.059954)
Cary         boring  0.000000   0.000000   0.000000 (  0.001004)