AtCoder Regular Contest 102
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Problem Statement
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You are given a permutation of $1,2,...,N$: $p_1,p_2,...,p_N$. Determine if the state where $p_i=i$ for every $i$ can be reached by performing the following operation any number of times:
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- Choose three elements
$p_{i-1},p_{i},p_{i+1}$($2\leq i\leq N-1$) such that$p_{i-1}>p_{i}>p_{i+1}$and reverse the order of these three.
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Constraints
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$3 \leq N \leq 3 × 10^5$$p_1,p_2,...,p_N$is a permutation of$1,2,...,N$.
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Input
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Input is given from Standard Input in the following format:
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N
p_1
:
p_N
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Output
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If the state where $p_i=i$ for every $i$ can be reached by performing the operation, print Yes; otherwise, print No.
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样例
Input #1
5
5
2
1
4
3
Output #1
Yes
The state where $p_i=i$ for every $i$ can be reached as follows:
- Reverse the order of $p_1,p_2,p_3$. The sequence $p$ becomes $1,2,5,4,3$.
- Reverse the order of $p_3,p_4,p_5$. The sequence $p$ becomes $1,2,3,4,5$.
Input #2
4
3
2
4
1
Output #2
No
Input #3
7
3
2
1
6
5
4
7
Output #3
Yes
Input #4
6
5
3
4
1
2
6
Output #4
No
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。