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