Step 1: Divide the number into separate digits:
7307 => 7 3 0 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 3 => 4
3 to 0 => 3
0 to 7 => 7
7 to 7 => 0
Step 3: Convert distances to codes (0=E[qual],
1 & 9 = C[onsecutive], 2-8 = N[one]):
4 => N
3 => N
7 => N
0 => E
Step 4: Combine the filters to a string:
N N N E = NNNE