I am having problem understanding how we are utilising Binary Indexed tree to solve the problem.The DFS part is clear as well as the notion of levels. But i am unable to understand how BIT is used. http://codeforces.com/contest/383/problem/C link.

Hey i am getting wrong answer on amazing maze http://www.spoj.com/problems/DCEPC701/

my code http://ideone.com/B62iqc I am unable to find the error.Hope someone help me.