258. Add Digits

Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.

Example:

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

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

# @lc code=start
using LeetCode

function add_digits(num::Int)::Int
    num <= 9 && return num
    return iszero(num % 9) ? 9 : num % 9
end
# @lc code=end

add_digits (generic function with 1 method)

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