Step 1: Divide the number into separate digits:
0709 => 0 7 0 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 7 => 7
7 to 0 => 7
0 to 9 => 9
9 to 0 => 9
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
7 => N
7 => N
9 => C
9 => C
Step 4: Combine the filters to a string:
N N C C = NNCC