[BOJ 15326] Usmjeri
View as PDFWe are given a tree1 with N nodes denoted with different positive integers from 1 to N. Additionally, you are given M node pairs from the tree in the form of (a1, b1), (a2, b2), …, (aM, bM).</p>
We need to direct each edge of the tree so that for each given node pair (ai, bi) there is a path from ai to bi or from bi to ai. How many different ways are there to achieve this? Since the solution can be quite large, determine it modulo 109 + 7.
1A tree is a graph that consists of N nodes and N - 1 edges such that there exists a path from each node to each other node.
입력 형식
The first line of input contains the positive integers N and M (1 ≤ N, M ≤ 3·105), the number of nodes in the tree and the number of given node pairs, respectively.</p>
Each of the following N - 1 lines contains two positive integers, the labels of the nodes connected with an edge.
The i th of the following M lines contains two different positive integers ai and bi , the labels of the nodes from the i th node pair. All node pairs will be mutually different.
출력 형식
You must output a single line containing the total number of different ways to direct the edges of the tree that meet the requirement from the task, modulo 109 + 7.
예제 입력 1
4 1
1 2
2 3
3 4
2 4
예제 출력 1
4
예제 입력 2
7 2
1 2
1 3
4 2
2 5
6 5
5 7
1 7
2 6
예제 출력 2
8
예제 입력 3
4 3
1 2
1 3
1 4
2 3
2 4
3 4
예제 출력 3
0
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