Step 1: Divide the number into separate digits:
1111 => 1 1 1 1
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
1 to 1 = 0
1 to 1 = 0
1 to 1 = 0
1 to 1 = 0
Step 3: Combine the filters to a string:
0 0 0 0 = 0000