시간 제한메모리 제한제출정답맞힌 사람정답 비율
1 초 1024 MB53141432.558%

문제

$N \le 2\,000$을 만족하는 노드 $N$개의 트리 $T$가 주어진다. 다음의 조건을 만족하는 트리 $T'$를 구성하여 출력하자.

  • $T'$의 크기를 $M$이라 하자. $M$은 $N$ 이상 $22\,000$ 이하여야 한다. 즉, $N \le M \le 22\,000$이여야 한다.
  • $T'$은 이진 트리이여야 한다. 즉, $T'$의 모든 노드는 $3$개 이하의 다른 노드들과 연결되어야 한다.
  • $\text{dist}(u, v)$를 $T$에서 $u$번 노드와 $v$번 노드 사이의 거리로 정의하자. 비슷하게, $T'$에 대해서 $\text{dist}'(u, v)$를 $u$번 노드와 $v$번 노드의 거리로 정의하자.
  • $1 \le u, v, p, q \le N$에 대해 $\text{dist}'(u, v) = \text{dist}'(p, q)$이면 $\text{dist}(u, v) = \text{dist}(p, q)$이여야 한다.

입력

첫째 줄에 $N$이 주어진다.

둘째 줄부터 $N-1$개의 줄에 걸쳐 $T$의 각 간선의 양 끝점의 번호가 한 줄에 공백으로 구분되어 주어진다.

출력

첫째 줄에 $M$을 출력한다.

둘째 줄부터 $M-1$개의 줄에 걸쳐 $T'$의 각 간선의 양 끝점의 번호를 한 줄에 공백으로 구분하여 출력한다.

제한

  • $2 \le N \le 2\,000$

서브태스크

번호배점제한
14

$N \le 10$

28

$N \le 20$

311

$N \le 100$

422

$N \le 1\,000$

555

추가적인 제약 조건이 없다.

예제 입력 1

6
1 2
2 3
3 4
3 5
3 6

예제 출력 1

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

노트

트리는 임의의 두 정점 사이의 단순 경로가 유일하게 존재하는 연결 그래프를 말한다.

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

출처

University > KAIST > KAIST RUN Spring Contest > 2025 KAIST RUN Spring Contest H번

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