Step 1: Divide the number into separate digits:
5549 => 5 5 4 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 5 = 0
5 to 4 = 1
4 to 9 = 5
9 to 5 = 4
Step 3: Combine the filters to a string:
0 1 5 4 = 0154