CF1328E · Tree Queries

• 难度：1900
• 标签：dfs and similar、graphs、trees
• 链接：https://codeforces.com/problemset/problem/1328/E
• 时间限制：2 seconds　内存限制：256 megabytes
• 出现位置：Day29-阶段模拟8-高压综合卷

英文原题面

Statement

You are given a rooted tree consisting of $n$ vertices numbered from $1$ to $n$. The root of the tree is a vertex number $1$. A tree is a connected undirected graph with $n-1$ edges. You are given $m$ queries. The $i$-th query consists of the set of $k_i$ distinct vertices $v_i[1], v_i[2], \dots, v_i[k_i]$. Your task is to say if there is a path from the root to some vertex $u$ such that each of the given $k$ vertices is either belongs to this path or has the distance $1$ to some vertex of this path.

Input

The first line of the input contains two integers $n$ and $m$ ($2 \le n \le 2 \cdot 10^5$, $1 \le m \le 2 \cdot 10^5$) — the number of vertices in the tree and the number of queries. Each of the next $n-1$ lines describes an edge of the tree. Edge $i$ is denoted by two integers $u_i$ and $v_i$, the labels of vertices it connects $(1 \le u_i, v_i \le n, u_i \ne v_i$). It is guaranteed that the given edges form a tree. The next $m$ lines describe queries. The $i$-th line describes the $i$-th query and starts with the integer $k_i$ ($1 \le k_i \le n$) — the number of vertices in the current query. Then $k_i$ integers follow: $v_i[1], v_i[2], \dots, v_i[k_i]$ ($1 \le v_i[j] \le n$), where $v_i[j]$ is the $j$-th vertex of the $i$-th query. It is guaranteed that all vertices in a single query are distinct. It is guaranteed that the sum of $k_i$ does not exceed $2 \cdot 10^5$ ($\sum\limits_{i=1}^{m} k_i \le 2 \cdot 10^5$).

Output

For each query, print the answer — "YES", if there is a path from the root to some vertex $u$ such that each of the given $k$ vertices is either belongs to this path or has the distance $1$ to some vertex of this path and "NO" otherwise.

样例

样例 1

输入：

10 6
1 2
1 3
1 4
2 5
2 6
3 7
7 8
7 9
9 10
4 3 8 9 10
3 2 4 6
3 2 1 5
3 4 8 2
2 6 10
3 5 4 7

输出：

YES
YES
YES
YES
NO
NO

样例解释（英文原文）

The picture corresponding to the example:

Consider the queries. The first query is $[3, 8, 9, 10]$. The answer is "YES" as you can choose the path from the root $1$ to the vertex $u=10$. Then vertices $[3, 9, 10]$ belong to the path from $1$ to $10$ and the vertex $8$ has distance $1$ to the vertex $7$ which also belongs to this path. The second query is $[2, 4, 6]$. The answer is "YES" as you can choose the path to the vertex $u=2$. Then the vertex $4$ has distance $1$ to the vertex $1$ which belongs to this path and the vertex $6$ has distance $1$ to the vertex $2$ which belongs to this path. The third query is $[2, 1, 5]$. The answer is "YES" as you can choose the path to the vertex $u=5$ and all vertices of the query belong to this path. The fourth query is $[4, 8, 2]$. The answer is "YES" as you can choose the path to the vertex $u=9$ so vertices $2$ and $4$ both have distance $1$ to the vertex $1$ which belongs to this path and the vertex $8$ has distance $1$ to the vertex $7$ which belongs to this path. The fifth and the sixth queries both have answer "NO" because you cannot choose suitable vertex $u$.