Algorithm 4 Exception handling algorithm
Input: all nodes' neighborhood N; verified permutation S
Output: node location permutation S.
1.	use Alogorithm1 to derive the reverse verification permutation S1
2.	k = the number of ordering S1; n = the actual node number
3.	If k = = n then
4.	If S1 is reversion of S then
5.	S = S
6.	else
7.	S = null
8.	end if
9.	else if n – k = = 1 then
10.	turn to Algorithm 2 using S1 as input
11.	else
12.	turn to Algorithm 3 using S1 as input
13.	end if