算法系列（9） LeetCode256

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?

/**
* @param {number} num
* @return {number}
*/
var addDigits = function(num) {

while(num.toString().length>1){
var sum=0;
while(num!=0){
sum += num%10;
num = ~~(num/10);
}
num = sum;
}
return num;
};