Hi I am currently trying to solve my first problem with segment tree. Link to the problem:http://www.hackerearth.com/tracks/pledge-2015-medium/xor-in-tree-1/

I couldn't understand the segment tree implementation in context to this problem which is present in the editorial in the problem setter's solution.

What does T[i] store here?

For the second query, why

int res = path_xor[u] ^ path_xor[v] ^ ST.get_xor(pos[u]) ^ ST.get_xor(pos[v]) ^ a[c];

and not

int res = ST.get_xor(pos[u]) ^ ST.get_xor(pos[v]) ^ a[c]; for the second query?

Currently, I could only understand that the tree is first ordered so that it becomes inline ie topological sort.Now the segment tree works on this topologically sorted tree.

Hi This is my first post.I was trying to solve the Tree Coloring problem on hackerearth.com.

Problem Link:http://www.hackerearth.com/problem/algorithm/tree-coloring/

I'm having difficulty in understanding the editorial of the above problem.

Could somebody explain me why

F[i] = C(S[i], S[c_1]) * C(S[i]-S[c_1], S[c2]) * .. * C(S[i]-S[c_1]-S[c_2] — .. — S[c_(k-1)], S[c_k]) * F[c_1] * F[c_2] * .. *F[c_k], where C(n, k) denoting binomial coefficient (n, k), that means C(n, k) = n! / ((n-k)! * k!)?`

I was only able to understand the F[c_1] * F[c_2] * .. *F[c_k] part.

But was unable to understand the reason behind

C(S[i], S[c_1]) * C(S[i]-S[c_1],S[c2]) * .. * C(S[i]-S[c_1]-S[c_2]-S[c_(k-1)], S[c_k]).