Check if a number is divisible by 3

Question

I need to find whether a number is divisible by 3 without using %, / or *. The hint given was to use atoi() function. Any

Answer 1

My solution in Java only works for 32-bit unsigned ints.

static boolean isDivisibleBy3(int n) {
  int x = n;
  x = (x >>> 16) + (x & 0xffff); // max 0x0001fffe
  x = (x >>> 8) + (x & 0x00ff); // max 0x02fd
  x = (x >>> 4) + (x & 0x000f); // max 0x003d (for 0x02ef)
  x = (x >>> 4) + (x & 0x000f); // max 0x0011 (for 0x002f)
  return ((011111111111 >> x) & 1) != 0;
}

It first reduces the number down to a number less than 32. The last step checks for divisibility by shifting the mask the appropriate number of times to the right.