digital root method

maths/sum_of_digits.py

@@ -55,9 +55,32 @@ def sum_of_digits_compact(n: int) -> int:
  return sum(int(c) for c in str(abs(n)))
 
 
+def digital_root(n: int) -> int:
+ """
+ finding the digital root of n
+ https://en.wikipedia.org/wiki/Digital_root
+
+ >>> digital_root(394328)
+ 2
+ >>> digital_root(-394328)
+ -1
+ >>> digital_root(123)
+ 6
+ >>> digital_root(0)
+ 0
+ >>> digital_root("109820394")
+ -1
+ """
+
+ try:
+ return n % 9 or n and 9 if n >= 0 else -1
+ except TypeError:
+ return -1
+
+
 def benchmark() -> None:
  """
- Benchmark code for comparing 3 functions,
+ Benchmark code for comparing 4 functions,
  with 3 different length int values.
  """
  print("\nFor small_num = ", small_num, ":")
@@ -85,6 +108,14 @@ def benchmark() -> None:
  timeit("z.sum_of_digits_compact(z.small_num)", setup="import __main__ as z"),
  "seconds",
  )
+ print(
+ "> digital_root()",
+ "\tans =",
+ digital_root(small_num),
+ "\ttime =",
+ timeit("z.digital_root(z.small_num)", setup="import __main__ as z"),
+ "seconds",
+ )
 
  print("\nFor medium_num = ", medium_num, ":")
  print(
@@ -111,6 +142,14 @@ def benchmark() -> None:
  timeit("z.sum_of_digits_compact(z.medium_num)", setup="import __main__ as z"),
  "seconds",
  )
+ print(
+ "> digital_root()",
+ "\t\tans =",
+ digital_root(medium_num),
+ "\ttime =",
+ timeit("z.digital_root(z.medium_num)", setup="import __main__ as z"),
+ "seconds",
+ )
 
  print("\nFor large_num = ", large_num, ":")
  print(
@@ -137,6 +176,14 @@ def benchmark() -> None:
  timeit("z.sum_of_digits_compact(z.large_num)", setup="import __main__ as z"),
  "seconds",
  )
+ print(
+ "> digital_root()",
+ "\tans =",
+ digital_root(large_num),
+ "\ttime =",
+ timeit("z.digital_root(z.large_num)", setup="import __main__ as z"),
+ "seconds",
+ )
 
 
 if __name__ == "__main__":