Codeforces Global Round 1
F
Nearest Leaf
Codeforces
2600
原题
← EG →
翻译中…

Let's define the Eulerian traversal of a tree (a connected undirected graph without cycles) as follows: consider a depth-first search algorithm which traverses vertices of the tree and enumerates them in the order of visiting (only the first visit of each vertex counts). This function starts from the vertex number $1$ and then recursively runs from all vertices which are connected with an edge with the current vertex and are not yet visited in increasing numbers order. Formally, you can describe this function using the following pseudocode:

翻译中…

next_id = 1
id = array of length n filled with -1
visited = array of length n filled with false

function dfs(v):
    visited[v] = true
    id[v] = next_id
    next_id += 1
    for to in neighbors of v in increasing order:
        if not visited[to]:
            dfs(to)

翻译中…

You are given a weighted tree, the vertices of which were enumerated with integers from $1$ to $n$ using the algorithm described above.

翻译中…

A leaf is a vertex of the tree which is connected with only one other vertex. In the tree given to you, the vertex $1$ is not a leaf. The distance between two vertices in the tree is the sum of weights of the edges on the simple path between them.

翻译中…

You have to answer $q$ queries of the following type: given integers $v$, $l$ and $r$, find the shortest distance from vertex $v$ to one of the leaves with indices from $l$ to $r$ inclusive.

翻译中…

Input

翻译中…

The first line contains two integers $n$ and $q$ ($3 \leq n \leq 500\,000, 1 \leq q \leq 500\,000$) — the number of vertices in the tree and the number of queries, respectively.

翻译中…

The $(i - 1)$-th of the following $n - 1$ lines contains two integers $p_i$ and $w_i$ ($1 \leq p_i \lt i, 1 \leq w_i \leq 10^9$), denoting an edge between vertices $p_i$ and $i$ with the weight $w_i$.

翻译中…

It's guaranteed that the given edges form a tree and the vertices are enumerated in the Eulerian traversal order and that the vertex with index $1$ is not a leaf.

翻译中…

The next $q$ lines describe the queries. Each of them contains three integers $v_i$, $l_i$, $r_i$ ($1 \leq v_i \leq n, 1 \leq l_i \leq r_i \leq n$), describing the parameters of the query. It is guaranteed that there is at least one leaf with index $x$ such that $l_i \leq x \leq r_i$.

翻译中…

Output

翻译中…

Output $q$ integers — the answers for the queries in the order they are given in the input.

翻译中…

Note

翻译中…

In the first example, the tree looks like this:

翻译中…

image

翻译中…

In the first query, the nearest leaf for the vertex $1$ is vertex $4$ with distance $3$. In the second query, the nearest leaf for vertex $5$ is vertex $5$ with distance $0$. In the third query the nearest leaf for vertex $4$ is vertex $4$; however, it is not inside interval $[1, 2]$ of the query. The only leaf in interval $[1, 2]$ is vertex $2$ with distance $13$ from vertex $4$.

翻译中…

样例

Input #1
5 3
1 10
1 1
3 2
3 3
1 1 5
5 4 5
4 1 2
Output #1
3
0
13
InputCopy OutputCopy
Input #2
5 3
1 1000000000
2 1000000000
1 1000000000
1 1000000000
3 4 5
2 1 5
2 4 5
Output #2
3000000000
1000000000
2000000000
InputCopy OutputCopy
Input #3
11 8
1 7
2 1
1 20
1 2
5 6
6 2
6 3
5 1
9 10
9 11
5 1 11
1 1 4
9 4 8
6 1 4
9 7 11
9 10 11
8 1 11
11 4 5
Output #3
8
8
9
16
9
10
0
34
InputCopy OutputCopy
题目信息
题号
1110F
时间限制
4 s
内存限制
512 MB
标签
数据结构
树

题面与样例版权归 Codeforces 及出题人所有;中文翻译由 AI 生成(CI 管线),如有出入请以原文为准。