Add Digits Python Solution with Tests

Tested Python solution for LeetCode 258 with 17 pytest cases. Generate a practice environment with lcpy.

LeetCode 258, Easy. Topics: Math, Simulation, Number Theory. View on LeetCode.

Generate this problem as a practice environment: tested reference solution, 17 parametrized pytest cases, and a playground notebook:

lcpy gen -n 258   # by problem number
lcpy gen -s add_digits   # by problem name

​

Problem

Given an integer num, repeatedly add all its digits until the result has only one digit, and return it.

​

Examples

Input: num = 38
Output: 2
Explanation: The process is
38 --> 3 + 8 --> 11
11 --> 1 + 1 --> 2
Since 2 has only one digit, return it.

Input: num = 0
Output: 0

​

Constraints

• 0 <= num <= 2^31 - 1

Follow up: Could you do it without any loop/recursion in O(1) runtime?

​

Solution

Reference implementation from solution.py on GitHub, full suite in test_solution.py:

class Solution:
    # Time: O(1) (at most 3 passes for 32-bit inputs)
    # Space: O(1)
    def add_digits(self, num: int) -> int:
        if num == 0:
            return 0
        return 1 + (num - 1) % 9

​

Complexity

Time	Space
O(1) (at most 3 passes for 32-bit inputs)	O(1)

​

Tags