Step 1: Divide the number into separate digits:
3369 => 3 3 6 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 3 = 0
3 to 6 = 3
6 to 9 = 3
9 to 3 = 6
Step 3: Combine the filters to a string:
0 3 3 6 = 0336