NOI '20 P2 - Destiny
View as PDFGiven a tree  (
 is the set of vertices and 
 is the set
of edges) and a set of pairs of vertices 
satisfying for all 
, 
 and 
 is an ancestor of
 on tree 
, you are supposed to compute how many functions
 (i.e. for each edge 
, the value of
 would be either 
 or 
) satisfies the condition for any
 there exists an edge 
 on the path from 
 to 
 such
that 
. Output the answer modulo 
.
Input Specification
The first line contains an input  denoting the number of
vertices in tree 
. The nodes are numbered from 1 to 
 and the root
node is node 1. In the following 
 lines, each line contains two
integers separated by a space 
 such that
 denoting there exists an edge on the tree
between node 
 and 
. There are no guarantees for the direction
of the edge. The following line contains an integer 
 denoting the
size of 
. In the following 
 lines, each line contains two integers
separated by a space 
 denoting 
. There may be
duplication, or in other words, there might exist some 
 such
that 
 and 
.
Output Specification
The output contains only an integer denoting the number of
functions  satisfying the condition above.
Sample Input 1
5
1 2
2 3
3 4
3 5
2
1 3
2 5
Sample Output 1
10
Sample Input 2
15
2 1
3 1
4 3
5 2
6 3
7 6
8 4
9 5
10 7
11 5
12 10
13 3
14 9
15 8
6
3 12
5 11
2 5
3 13
8 15
1 13
Sample Output 2
960
Constraints
For all test cases, , 
.
The input forms a tree, where for all , 
 is the ancestor of 
.
| Test Case | Additional Constraints | ||
|---|---|---|---|
| 1 | None. | ||
| 2 | |||
| 3 | |||
| 4 | |||
| 5 | |||
| 6 | |||
| 7 | |||
| 8 | |||
| 9 | |||
| 10 | |||
| 11 | |||
| 12 | |||
| 13 | |||
| 14 | |||
| 15 | |||
| 16 | |||
| 17 | See below. | ||
| 18 | |||
| 19 | None. | ||
| 20 | |||
| 21 | |||
| 22 | |||
| 23 | |||
| 24 | |||
| 25 | 
In this problem, a perfect binary tree is a binary tree such that each non-leaf node has two children and the depths of all leaf nodes are the same; if we number the nodes in a perfect binary tree from up to down, from left to right, the tree formed by the nodes with smallest numbers form a complete binary tree. Test cases 17 and 18 are complete binary trees.
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