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?
Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.
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Code:
int addDigits(int num) {
return 1+(num-1)%9;
}
原文：http://www.cnblogs.com/Alex0111/p/5373628.html