# Tree Decomposition (width 2)

AC一覧

## Problem Statement問題文

You are given a simple, undirected graph with $N$ vertices and $M$ edges. Its edges are $(u_i, v_i)$.

Determine whether the tree width of the graph is no more than 2. If it is, construct a tree decomposition with tree width no more than 2.

In other words, construct a tree with $K$ vertices, and the bag (subset of vertices in the original graph) $B_0, B_1, \cdots, B_{K - 1}$ on each of its vertices.

• $0 \leq K \leq 10N + M + 10$
• For each edge $(u_i, v_i)$, there is a bag that contains both $u_i, v_i$.
• For each vertex $i$ in the original graph, all vertices in the tree whose bag contains vertex $i$ are connected.

$N$ 頂点 $M$ 辺の単純な無向グラフが与えられる。辺は $(u_i, v_i)$。

つまり、以下の条件を満たす $K$ 頂点の木と、その各頂点にバッグ(=元のグラフの頂点の部分集合) $B_0, B_1, \cdots, B_{K - 1}$ を構築してください。

• $0 \leq K \leq 10N + M + 10$
• すべての辺 $(u_i, v_i)$ について、$u_i, v_i$ を両方含むバッグが存在する
• 元のグラフの各頂点 $i$ について、バッグに頂点 $i$ を含むような木の頂点のみを取り出すと、この頂点らは連結になっている

## Constraints制約

• $1 \leq N \leq 500{,}000$
• $0 \leq M \leq 500{,}000$
• The graph is simple.
• $1 \leq N \leq 500{,}000$
• $0 \leq M \leq 500{,}000$
• グラフは単純

## Input入力

Input and output are in the format used in PACE 2017 Track A. Also refer to the samples.

p tw $N$ $M$
$u_1$ $v_1$
$u_2$ $v_2$
$\vdots$
$u_M$ $v_M$


Note that $u_i, v_i$ are 1-indexed.

$u_i, v_i$ は 1-indexed なことに注意せよ

## Output出力

If the tree width is $3$ or larger, output $-1$ in the first line. (This is not the format used in PACE 2017 Track A)

Otherwise, output in the following format.

そうでない場合以下の形式で出力してください。

s td $K$ $w$ $N$
b $1$ $v$ $\ldots$ $v$
b $2$ $v$ $\ldots$ $v$
$\vdots$
b $K$ $v$ $\ldots$ $v$
$a_1$ $b_1$
$a_2$ $b_2$
$a_{K - 1}$ $b_{K - 1}$

• $K$ is the number of vertices in the tree.
• $a_i$, $b_i$ are edges in the tree. Note that they are 1-indexed.
• $w$ is an integer no more than 2. It is the size of the tree decomposition. It is acceptable to always output $2$ for it, but it is also fine to output $0, 1$ when appropriate. (For example, for testing a stronger library)
• The $1 + i$-th line contains the information of a bag. $v$ is a 1-indexed vertex ID in the original graph. Each line contains at most $w + 1$ vertices $v$.
• $K$ は木の頂点数
• $a_i$, $b_i$ は木の辺。1-indexed なことに注意せよ
• $w$ は $2$ 以下の整数。木分解のサイズを表す。$2$ を出力しておけば問題ないが、(たとえばより強いライブラリのテストのために) $0, 1$ を出力しても良い。
• $1 + i$ 行目はバッグの情報を表す。$v$ は 1-indexed の元のグラフの頂点番号、各行ごとに $v$ の個数は $w + 1$ 個以下

## Sampleサンプル

### # 1

p tw 5 6
1 2
2 3
3 4
4 5
2 4
4 1

s td 5 2 5
b 1 5
b 2 4 5
b 3 3 4
b 4 2 3 4
b 5 1 2 4
1 2
2 3
3 4
4 5


### # 2

p tw 4 6
1 2
1 3
1 4
2 3
2 4
3 4

-1


Timelimit: 10 secs

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