Subtree Center solution codechef

Subtree Center solution codechef

You are given a tree with NN nodes (numbered 11 through NN) and QQ queries (numbered 11 through QQ). For each valid ii, in the ii-th query, you are given KiKi nodes x1,x2,,xKix1,x2,…,xKi. Consider the smallest subtree which contains all of these nodes; you should find all centers of this subtree.

A node is called a center of a tree if it lies in the middle of at least one longest path in that tree. Note that there may be multiple longest paths (paths with the same maximum length) and for a longest path which contains an even number of nodes, there are two nodes lying in the middle of this path.

Input Subtree Center solution codechef

  • The first line of the input contains a single integer TT denoting the number of test cases. The description of TT test cases follows.
  • The first line of each test case contains two space-separated integers NN and QQ.
  • N1N−1 lines follow. For each valid ii, the ii-th of these lines contains two space-separated integers uu and vv denoting that there is an edge between nodes uu and vv in the tree.
  • QQ more lines follow. For each valid ii, the ii-th of these lines contains an integer KiKi, followed by a space and KiKi space-separated integers x1,x2,,xKix1,x2,…,xKi.

Note: The input and output of this problem are large, so prefer using fast input/output methods.

Output Subtree Center solution codechef

For each query, print a single line containing an integer CC denoting the number of centers, followed by a space and CC space-separated integers — the nodes which are centers of the given subtree, sorted in increasing order.

Constraints Subtree Center solution codechef

  • 1T1051≤T≤105
  • 1N1051≤N≤105
  • 1u,vN1≤u,v≤N
  • the graph described on the input is a tree
  • 1Q1061≤Q≤106
  • 1xiN1≤xi≤N for each valid ii
  • for each query, x1,x2,,xKix1,x2,…,xKi are pairwise distinct
  • the sum of NN over all test cases does not exceed 51055⋅105
  • the sum of KiKi over all queries in all test cases does not exceed 106106

Example Input Subtree Center solution codechef

3 2
1 2
2 3
2 1 3
2 1 2
5 2
1 2
2 3
2 4
3 5
1 2
2 4 5

Example Output Subtree Center solution codechef

1 2
2 1 2
1 2
2 2 3

Explanation Subtree Center solution codechef

Example case 1: The figure below describes the second query. The smallest subtree containing the given nodes is coloured red and the nodes which are its centers are coloured blue.

Example case 2: The figure below describes the second query with subtree and centers coloured in the same way.


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