Fold the Digits Down to One

Easy

You are given a non-negative integer n. While it has more than one digit, replace it with the sum of its digits. Return the single digit you end up with. Can you do it in O(1), with no loops or recursion?

Example 1

n=4975 → 7

4 + 9 + 7 + 5 = 25, then 2 + 5 = 7, a single digit.

Example 2

n=6 → 6

The number already has one digit, so there is nothing to add.

Example 3

n=99 → 9

9 + 9 = 18, then 1 + 8 = 9.

Constraints

0 ≤ n ≤ 2³¹ − 1

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Topics

Math Number Theory Simulation

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Input

n=4975

Expected

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