Step 1: Divide the number into separate digits:
1120 => 1 1 2 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 1 = 0
1 to 2 = 1
2 to 0 = 2
0 to 1 = 1
Step 3: Combine the filters to a string:
0 1 2 1 = 0121