Codeforces Round 637 (Div. 1) - Thanks, Ivan Belonogov!
E
Nastya and Bees
Codeforces
未评级
原题
← DF →
翻译中…

Unfortunately, a mistake was found in the proof of the author's solution to this problem. Currently, we don't know the absolutely correct solution. However, you can solve this task, but if your solution passes all the tests, it is not guaranteed to be correct. If your solution has passed all the tests and you are sure that it is correct, you can write to one of the contest authors about it.

翻译中…
  • Surely you all read the book "Alice in Wonderland". In this task, Nastya got to the country of Three strange Bees. The bees are strange because their honeycombs are pentagonal. Nastya got there illegally, so she wants bees not to catch her. Help the bees punish the intruder! *
翻译中…

This is an interactive problem.

翻译中…

A beehive is a connected undirected graph where bees and Nastya can move along the edges. A graph satisfies two properties:

翻译中…
  • The degree of any of its vertex is no more than $3$.
  • For each edge, there exists a cycle of length not greater than $5$ passing through this edge.
翻译中…

There are three bees and Nastya. You play for bees. Firstly, you choose the vertices where you put the bees. Then Nastya chooses another vertex in which she will initially appear. One move is first moving the bees, then Nastya, in turn:

翻译中…
  1. For each of your bees, you can either move each one along some edge from the vertex they are currently staying or leave it in place.
  2. Then Nastya will necessarily move along some edge of the graph from the vertex she is currently staying/.
翻译中…

You win if at least one of the bees and Nastya are in the same vertex at any time of the game.

翻译中…

If this situation does not occur after $n$ moves, then you lose.

翻译中…

Several bees can be in the same vertex.

翻译中…

Input

翻译中…

The first line contains two integers $n$ $(4 \leq n \leq 5000)$ and $m$ $(n \leq m \leq 3n)$  — the number of vertices and edges in the graph.

翻译中…

Each of the next $m$ lines contains two integers $v$ and $u$ $(1 \leq v, u \leq n)$, which mean that there is an edge between the vertices $v$ and $u$. It is guaranteed that the graph is connected, does not contain loops that the degree of any vertex does not exceed $3$ and a cycle of length no more than $5$ passes through each edge. Note that the graph may contain multiple edges.

翻译中…

Interaction

翻译中…

At each turn, you must output exactly three vertices $a, b, c$ $(1 \leq a, b, c \leq n)$. For the first time, $3$ vertices displayed will indicate which vertices you originally placed bees on. In response, you will receive the vertex where the jury placed Nastya. Each next $3$ vertices will indicate where the $3$ bees move at your turn. Each of the bees can, regardless of other bees, both remain at the current vertex and move along the edge. After the next output of $3$ vertices, in response, you get the number of the new vertex to which Nastya went.

翻译中…

As soon as one of the bees is at the same vertex with Nastya or you have reached the limit on the number of moves, your program should stop working. That is if you made a move, and one of the bees ended up at the same vertex with Nastya, your program must stop working, or if Nastya made a move and ended up at the same vertex with one of the bees, you should not make your move and the program should stop working.

翻译中…

If the number of moves exceeds limit ($n$, where $n$ is the number of vertices), you will get the Wrong Answer verdict.

翻译中…

Your solution may receive the verdict Idleness Limit Exceeded if you don't output anything or forget to flush the output buffer.

翻译中…

To flush the output buffer, you need to do the following immediately after printing the query and the line end:

翻译中…
  • fflush(stdout) or cout.flush() in C++;
  • System.out.flush() in Java;
  • flush(output) in Pascal;
  • stdout.flush() in Python;
  • for other languages see documentation.
翻译中…

In this problem interactor is adaptive. This means that depending on all your previous moves, Nastya's behavior may change.

翻译中…

Hacks are not available for this problem.

翻译中…

Note

翻译中…

Let Nastya be a green chip, and three numbered red ones are three bees.

翻译中…

In the first test, the movement of the heroes looks like this.

翻译中…

image After selecting the starting vertices.

翻译中…

image The first move after the bees move.

翻译中…

image The first move after the Nastya's move. The first bee caught Nastya.

翻译中…

In the second test, the movement of the heroes looks like this.

翻译中…

image After selecting the starting vertices.

翻译中…

image The first move after the bees move.

翻译中…

image The first move after the Nastya's move.

翻译中…

image The second move after the bees move. The first bee caught Nastya.

翻译中…

样例

Input #1
5 5
1 2
2 3
3 4
4 5
5 1
4
5
Output #1
1 1 2
1 5 3
InputCopy OutputCopy
Input #2
8 9
1 2
2 3
3 4
4 5
5 1
5 6
6 7
7 8
8 4
1
5
Output #2
7 3 3
6 2 2
5 3 1
InputCopy OutputCopy
题目信息
题号
1340E
时间限制
1 s
内存限制
256 MB

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。