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?
Method 1.
class Solution {
public:
int addDigits(int num) {
if (num < 10)
return num;
while (num >= 10) {
int sum = 0;
while (num) {
sum += num%10;
num /= 10;
}
num = sum;
}
return num;
}
};
Method 2.
class Solution {
public:
int addDigits(int num) {
return (num - 1)%9 + 1;
}
};