Step 1: Divide the number into separate digits:
7118 => 7 1 1 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 1 = 6
1 to 1 = 0
1 to 8 = 7
8 to 7 = 1
Step 3: Combine the filters to a string:
6 0 7 1 = 6071