Step 1: Divide the number into separate digits:
5578 => 5 5 7 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
5 to 5 = 0
5 to 7 = 2
7 to 8 = 1
8 to 5 = 3
Step 3: Combine the filters to a string:
0 2 1 3 = 0213