Step 1: Divide the number into separate digits:
0987 => 0 9 8 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 9 = 9
9 to 8 = 1
8 to 7 = 1
7 to 0 = 7
Step 3: Combine the filters to a string:
9 1 1 7 = 9117