258.add-digits.cpp

/*
 * @lc app=leetcode id=258 lang=cpp
 *
 * [258] Add Digits
 *
 * https://leetcode.com/problems/add-digits/description/
 *
 * algorithms
 * Easy (54.73%)
 * Total Accepted:    251.1K
 * Total Submissions: 458.9K
 * Testcase Example:  '38'
 *
 * 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?
 */
class Solution {
public:
    int addDigits(int num) {
        while(num/10){
        	int cur = 0;
        	while(num)
        		cur+=num%10, num/=10;
        	num = cur;
        }
        return num;
    }
};