Step 1: Divide the number into separate digits:
1050 => 1 0 5 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 0 = 1
0 to 5 = 5
5 to 0 = 5
0 to 1 = 1
Step 3: Combine the filters to a string:
1 5 5 1 = 1551