258. Add Digits
Problem:
Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.
For example:
Given num = 38, 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?
Solutions:
public class Solution {
public int addDigits(int num) {
while (num >= 10) {
int sum = 0;
while (num != 0) {
sum += num % 10;
num = num / 10;
}
num = sum;
}
return num;
}
}
public class Solution {
public int addDigits(int num) {
return (num - 1) % 9 + 1;
}
}