Step 1: Divide the number into separate digits:
0945 => 0 9 4 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 9 = 9
9 to 4 = 5
4 to 5 = 1
5 to 0 = 5
Step 3: Combine the filters to a string:
9 5 1 5 = 9515