saxxi · August 16, 2015 11:29 · Aug 16, 2015
diff --git a/sum_digits.rb b/sum_digits.rb
@@ -0,0 +1,65 @@
+# Sum all the digits
+
+#   Write a program that takes a positive number as an input.
+#   The program should take every single digit of this number,
+#   and sum them until only a 1 digit number is left.
+
+#   Example input: 31337
+
+#   Output: 8 (because 3+1+3+3+7=17 and 1+7=8)
+
+#   Please add a benchmark for your solution.
+
+# Usage
+# > SumDigit.run 912931241291293124129129312412
+
+require 'inline'
+
+class SumDigit
+
+  def self.run_with_each_char(number) # 1st
+    while number > 9 do
+      sum = 0
+      number.to_s.each_char { |c| sum += c.to_i }
+      number = sum
+    end
+    number
+  end
+
+  def self.run_with_split(number) # 2nd
+    while number > 9 do
+      sum = 0
+      number.to_s.split('').each { |c| sum += c.to_i }
+      number = sum
+    end
+    number
+  end
+
+  def self.run_with_mod(number) # 3rd
+    while number > 9 do
+      sum = 0
+      while number > 0 do
+        sum += number % 10
+        number /= 10
+      end
+
+      number = sum
+    end
+    number
+  end
+
+  class << self
+    alias :run :run_with_each_char
+  end
+
+end
+
+require 'benchmark'
+
+test_number = 912923124541291293130241291290332124453534412745985591342932112041291209312411529720129312412349082109120942834938750395063473621032432480357565234
+
+Benchmark.bm do |x|
+  x.report { SumDigit.run_with_each_char test_number }
+  x.report { SumDigit.run_with_split test_number }
+  x.report { SumDigit.run_with_mod test_number }
+end
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