This notebook was prepared by Donne Martin. Source and license info is on GitHub.
* None input -> TypeError * negative input -> ValueError * 9 -> 9 * 138 -> 3 * 65536 -> 7
The naive solution simply isolates each digit with with modulo and integer division. We'll add each isolated digit to a list and sum the values.
138 % 10 = 8 -> isolated 138 // 10 = 13 13 % 10 = 3 -> isolated 13 // 10 = 1 1 % 10 = 1 -> isolated
A more optimal solution exists, by recognizing this is a digital root. See the Wikipedia article for more information.
Complexity:
class Solution(object):
def add_digits(self, num):
if num is None:
raise TypeError('num cannot be None')
if num < 0:
raise ValueError('num cannot be negative')
digits = []
while num != 0:
digits.append(num % 10)
num //= 10
digits_sum = sum(digits)
if digits_sum >= 10:
return self.add_digits(digits_sum)
else:
return digits_sum
def add_digits_optimized(self, num):
if num is None:
raise TypeError('num cannot be None')
if num < 0:
raise ValueError('num cannot be negative')
if num == 0:
return 0
elif num % 9 == 0:
return 9
else:
return num % 9
%%writefile test_add_digits.py
import unittest
class TestAddDigits(unittest.TestCase):
def test_add_digits(self, func):
self.assertRaises(TypeError, func, None)
self.assertRaises(ValueError, func, -1)
self.assertEqual(func(0), 0)
self.assertEqual(func(9), 9)
self.assertEqual(func(138), 3)
self.assertEqual(func(65536), 7)
print('Success: test_add_digits')
def main():
test = TestAddDigits()
solution = Solution()
test.test_add_digits(solution.add_digits)
try:
test.test_add_digits(solution.add_digits_optimized)
except NameError:
# Alternate solutions are only defined
# in the solutions file
pass
if __name__ == '__main__':
main()
Overwriting test_add_digits.py
%run -i test_add_digits.py
Success: test_add_digits Success: test_add_digits