258. Add Digits

Problem

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?

Problem Summary

Given a non-negative integer num, repeatedly add all the digits in each place until the result is a single digit.

Solution Approach

• Given a non-negative integer, repeatedly add the digits in each place until the result is a single digit, then output this single digit.
• Easy problem. Just loop and accumulate according to the problem statement.

Code

package leetcode

func addDigits(num int) int {
	for num > 9 {
		cur := 0
		for num != 0 {
			cur += num % 10
			num /= 10
		}
		num = cur
	}
	return num
}