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[leetcode] problem 258 – add digits

admin 11月 13, 2020 0

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.

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

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public int (int num) {        
    return num == 0 ? 0 : (num - 1) % 9 + 1;
}