Step 1: Divide the number into separate digits:
2211 => 2 2 1 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
2 to 2 = 0
2 to 1 = 1
1 to 1 = 0
1 to 2 = 1
Step 3: Combine the filters to a string:
0 1 0 1 = 0101