AtCoder Regular Contest 211 (Div. 2)
翻译中…
Problem Statement
翻译中…
You are given a positive integer $N$ and a permutation $P$ of $(1,2,\dots,N)$.
翻译中…
When there is a tree with $N$ vertices numbered $1,2,\dots,N$, Snuke and Takahashi move according to the following rules:
翻译中…
- Snuke specifies a permutation
$Q$of$(1,2,\dots,N)$such that the sequence returned by Takahashi, when following the rules below, is lexicographically maximum. - Takahashi, who is at vertex
$1$of the tree, first receives$Q$from Snuke and initializes an integer sequence$R$with the length-$1$sequence$(Q_1)$. Then, he moves$N-1$times as follows, and returns the final$R$: - Visit the vertex
$i$with the smallest$Q_i$among vertices that are adjacent to a previously visited vertex but have not yet been visited (it can be proved that there is always exactly one such vertex). Then, append$Q_i$to the end of$R$.
翻译中…
Here, vertex $1$ is considered to have been visited initially.
翻译中…
Determine whether there exists a tree such that Takahashi returns $P$.
翻译中…
You are given $T$ test cases; solve each of them.
翻译中…
Constraints
翻译中…
$1 \le T \le 10^5$$1 \le N \le 2 \times 10^5$$P$is a permutation of$(1,2,\dots,N)$.- The sum of
$N$over all test cases is at most$2 \times 10^5$. - All input values are integers.
翻译中…
Input
翻译中…
The input is given from Standard Input in the following format:
翻译中…
T
\text{case}_1
\text{case}_2
\vdots
\text{case}_T
翻译中…
Each test case is given in the following format:
翻译中…
N
P_1 P_2 \ldots P_N
翻译中…
Output
翻译中…
Output $T$ lines.
翻译中…
The $i$-th line should contain Yes if there exists a tree satisfying the conditions for the $i$-th test case, and No otherwise.
翻译中…
样例
Input #1
3
4
4 2 3 1
4
4 1 3 2
11
11 8 9 6 7 10 3 4 5 1 2
Output #1
Yes
No
Yes
For the first test case, a tree with four vertices having edges between vertices $1$-$2$, $1$-$3$, and $2$-$4$ satisfies the conditions.
If Snuke specifies $Q=(4,3,2,1)$, Takahashi visits vertices $1,3,2,4$ in this order and returns $R=(4,2,3,1)$. No matter what $Q$ Snuke specifies, it is impossible to make Takahashi return a sequence lexicographically larger than $(4,2,3,1)$, so the sequence that ends up being returned is $(4,2,3,1)$.
For the second test case, it can be proved that there is no tree satisfying the conditions.
题目信息
题面与样例版权归 AtCoder 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。