P25862 [AtCoder] Exactly K Steps
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题目描述

Problem Statement

You are given a tree with N vertices. The vertices are numbered $1, \dots, N$, and the $i-th (1 \leq i \leq N - 1) edge connects Vertices A_i$ and B_i.
We define the distance between Vertices u and v on this tree by the number of edges in the shortest path from Vertex u to Vertex v.
You are given Q queries. In the $i-th (1 \leq i \leq Q)$ query, given integers U_i and K_i, print the index of any vertex whose distance from Vertex U_i is exactly K_i. If there is no such vertex, print -1.

Input

Input is given from Standard Input in the following format:
N
A_1 B_1
$\vdots$
A_{N-1} B_{N-1}
Q
U_1 K_1
$\vdots$
U_Q K_Q

Output

Print Q lines. The $i-th (1 \leq i \leq Q)$ line should contain the index of any vertex whose distance from Vertex U_i is exactly K_i if such a vertex exists; if not, it should contain -1. If there are multiple such vertices, you may print any of them.

Constraints

  • $2 \leq N \leq 2 \times 10^5$
  • $1 \leq A_i \lt B_i \leq N$ $, (1 \leq i \leq N - 1)$
  • The given graph is a tree.
  • $1 \leq Q \leq 2 \times 10^5$
  • $1 \leq U_i, K_i \leq N$ $, (1 \leq i \leq Q)$
  • All values in input are integers.

Sample Input 1

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

Sample Output 1

4
1
-1

  • Two vertices, Vertices 4 and 5, have a distance exactly 2 from Vertex 2.
  • Only Vertex 1 has a distance exactly 3 from Vertex 5.
  • No vertex has a distance exactly 3 from Vertex 3.

Sample Input 2

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

Sample Output 2

2
4
10
-1
-1

输入格式

见题面 Input 部分

输出格式

见题面 Output 部分

样例输入
5 1 2 2 3 3 4 3 5 3 2 2 5 3 3 3
样例输出
4 1 -1