Logic to check the number is divisible by 3 or not?

Question

without using %, / or * , I have to find the no. is divisible by 3 or not?

it might be an interview question.

Thanks.

Answer 1

Here is a reasonably efficient algorithm for large numbers. (Well not very efficient, but reasonable given the constraints.)

Use sprintf to convert it to a string, convert each digit back to a number. Add up the digits. If you come up with 3, 6, or 9, it is divisible by 3. Anything else less than 10, it is not. Anything over 9, recurse.

For instance to test the number 813478902 you'd stringify, then add the digits to get 42, add those digits to get 6, so it is divisible by 3.