What can cause a "wrong answer" in 7-th test?

I used sqrt_decompostion and always get WA7.
what is tricky test 7?


I found my bug,  I renum all vertexes, but used old indexes :)  (renum all child of vertex to as id....id+k, sequencial indexes).

Edited by author 15.02.2012 18:35

Since description says p[i]<i it was tempting to assume that initial sequence is already in DFS order, but it's not necessarily so. Got RE7 when explicitly checked for this.