Solution: Add Digits
Explore how to solve the Add Digits problem by applying the mathematical concept of digital roots. This lesson guides you through using a constant time formula that avoids loops or recursion, enabling you to return a single digit sum efficiently. You'll gain understanding of the modular arithmetic behind this approach and implement a concise solution suitable for coding interviews.
We'll cover the following...
Statement
Given an integer num, repeatedly sum all of its digits until the resulting value is a single digit, then return that value.
Note: Could you solve this without any loop or recursion in
runtime?
Constraints:
num
Solution
The key insight behind this problem lies in a mathematical concept called the digital root. Rather than repeatedly summing digits in a loop, we can leverage the fact that any positive integer’s repeated digit sum is equivalent to