Step 1: Divide the number into separate digits:
3423 => 3 4 2 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
3 to 4 = 1
4 to 2 = 2
2 to 3 = 1
3 to 3 = 0
Step 3: Combine the filters to a string:
1 2 1 0 = 1210