Trying a Recursion problem (my first time)

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I'm trying to solve a Digital Root problem using Recursion. It seems to work for the first time around but not for the consecutive times. Here's what I want it to do:

digital_root(16)
=> 1 + 6
=> 7

digital_root(942)
=> 9 + 4 + 2
=> 15 ...
=> 1 + 5
=> 6

digital_root(132189)
=> 1 + 3 + 2 + 1 + 8 + 9
=> 24 ...
=> 2 + 4
=> 6

digital_root(493193)
=> 4 + 9 + 3 + 1 + 9 + 3
=> 29 ...
=> 2 + 9
=> 11 ...
=> 1 + 1
=> 2

Here's what I got:

def digital_root(n)
  arr = n.to_s.split("")
  arr.size > 1 ? arr[0].to_i + digital_root(arr[1..-1].join).to_i : arr.join.to_i
end

Let me know how to make it work regardless of how many layers I need. Thanks in advance.

recursion ruby
1 Answers

In your code, the function processes only 1 digits in 1 call. (4 for digital_root(493193))

Let's process 1 layer in 1 call and call next one (digital_root(29)).

def digital_root(n)
  arr = n.to_s.split("")
  arr.size > 1 ? digital_root(arr.map(&:to_i).sum) : arr.join.to_i
end

And slightly better version.

def digital_root(n)
  n < 10 ? n : digital_root(n.digits.sum)
end
user_15435790
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