Step 1: Divide the number into separate digits:
1191 => 1 1 9 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 1 = 0
1 to 9 = 8
9 to 1 = 8
1 to 1 = 0
Step 3: Combine the filters to a string:
0 8 8 0 = 0880