From 899eaf1d3a1b6624fb4454f40ec880ad1935788f Mon Sep 17 00:00:00 2001
From: Jessica Kwok <jessicatckwok@gmail.com>
Date: Wed, 17 Mar 2021 08:17:08 -0700
Subject: [PATCH 1/3] Add add digits challenge

---
 DIRECTORY.md                         |  1 +
 data_structures/arrays/add_digits.rb | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 data_structures/arrays/add_digits.rb

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 3c396ff..c14d5b6 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -4,6 +4,7 @@
 
 ## Data Structures
   * Arrays
+    * [Add Digits](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/add_digits.rb)
     * [Find All Duplicates In An Array](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/find_all_duplicates_in_an_array.rb)
     * [Find The Highest Altitude](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/find_the_highest_altitude.rb)
     * [Get Products Of All Other Elements](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/get_products_of_all_other_elements.rb)
diff --git a/data_structures/arrays/add_digits.rb b/data_structures/arrays/add_digits.rb
new file mode 100644
index 0000000..63e1d64
--- /dev/null
+++ b/data_structures/arrays/add_digits.rb
@@ -0,0 +1,24 @@
+# Challenge name: Add Digits
+#
+# Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.
+#
+# Example:
+#
+# Input: 38
+# Output: 2
+# Explanation: The process is like: 3 + 8 = 11, 1 + 1 = 2.
+#              Since 2 has only one digit, return it.
+#
+# Follow up:
+# Could you do it without any loop/recursion in O(1) runtime?
+# @param {Integer} num
+# @return {Integer}
+
+#
+# Approach 1: Brute Force
+#
+def add_digits(num)
+end
+
+puts(add_digits(38))
+# Output: 2
\ No newline at end of file

From 5588587bc1b22bf20af5b4278627f343400dd4f5 Mon Sep 17 00:00:00 2001
From: Jessica Kwok <jessicatckwok@gmail.com>
Date: Thu, 18 Mar 2021 08:55:05 -0700
Subject: [PATCH 2/3] Add recursion solution

---
 data_structures/arrays/add_digits.rb | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/data_structures/arrays/add_digits.rb b/data_structures/arrays/add_digits.rb
index 63e1d64..e18d768 100644
--- a/data_structures/arrays/add_digits.rb
+++ b/data_structures/arrays/add_digits.rb
@@ -15,10 +15,26 @@
 # @return {Integer}
 
 #
-# Approach 1: Brute Force
+# Approach 1: Recursion
+#
+# Time complexity: O(n)
 #
 def add_digits(num)
+  if num.to_s.length < 2
+    return num
+  end
+
+  digits_to_sum = num.to_s.split('')
+  sum = 0
+  digits_to_sum.each do |num|
+    sum += num.to_i
+  end
+
+  add_digits(sum)
 end
 
 puts(add_digits(38))
-# Output: 2
\ No newline at end of file
+# => 2
+
+puts(add_digits(284))
+# => 5
\ No newline at end of file

From fd3add587c806cc511eaa36265597108b15c8765 Mon Sep 17 00:00:00 2001
From: Jessica Kwok <jessicatckwok@gmail.com>
Date: Thu, 18 Mar 2021 13:15:19 -0700
Subject: [PATCH 3/3] Add solution without recursion

---
 data_structures/arrays/add_digits.rb | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/data_structures/arrays/add_digits.rb b/data_structures/arrays/add_digits.rb
index e18d768..731236d 100644
--- a/data_structures/arrays/add_digits.rb
+++ b/data_structures/arrays/add_digits.rb
@@ -33,6 +33,27 @@ def add_digits(num)
   add_digits(sum)
 end
 
+# puts(add_digits(38))
+# # => 2
+
+# puts(add_digits(284))
+# # => 5
+
+#
+# Approach 2: Without recursion
+#
+def add_digits(num)
+  until num.to_s.length < 2
+    digits_to_sum = num.to_s.split('')
+    num = 0
+
+    digits_to_sum.each do |number|
+      num += number.to_i
+    end
+  end
+  num
+end
+
 puts(add_digits(38))
 # => 2