Step 1: Divide the number into separate digits:
0787 => 0 7 8 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 7 = 7
7 to 8 = 1
8 to 7 = 1
7 to 0 = 7
Step 3: Combine the filters to a string:
7 1 1 7 = 7117