AtCoder Regular Contest 181
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Problem Statement
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You are given a permutation $P=(P_1,P_2,\dots,P_N)$ of $(1,2,\dots,N)$.
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You want to satisfy $P_i=i$ for all $i=1,2,\dots,N$ by performing the following operation zero or more times:
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- Choose an integer
$k$such that$1 \leq k \leq N$. If$k \geq 2$, sort the$1$-st through$(k-1)$-th terms of$P$in ascending order. Then, if$k \leq N-1$, sort the$(k+1)$-th through$N$-th terms of$P$in ascending order.
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It can be proved that under the constraints of this problem, it is possible to satisfy $P_i=i$ for all $i=1,2,\dots,N$ with a finite number of operations for any $P$. Find the minimum number of operations required.
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You have $T$ test cases to solve.
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Constraints
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$1 \leq T \leq 10^5$$3 \leq N \leq 2 \times 10^5$$P$is a permutation of$(1,2,\dots,N)$.- All input values are integers.
- The sum of
$N$across the test cases in a single input is at most$2 \times 10^5$.
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Input
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The input is given from Standard Input in the following format:
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T
\mathrm{case}_1
\vdots
\mathrm{case}_T
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Each case is given in the following format:
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N
P_1 P_2 \dots P_N
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Output
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Print $T$ lines. The $i$-th line should contain the answer for the $i$-th test case.
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样例
Input #1
3
5
2 1 3 5 4
3
1 2 3
7
3 2 1 7 5 6 4
Output #1
1
0
2
For the first test case,
- Performing the operation with $k=1$ results in $P$ becoming $(2,1,3,4,5)$.
- Performing the operation with $k=2$ results in $P$ becoming $(2,1,3,4,5)$.
- Performing the operation with $k=3$ results in $P$ becoming $(1,2,3,4,5)$.
- Performing the operation with $k=4$ results in $P$ becoming $(1,2,3,5,4)$.
- Performing the operation with $k=5$ results in $P$ becoming $(1,2,3,5,4)$.
Specifically, performing the operation with $k=3$ results in $P$ satisfying $P_i=i$ for all $i=1,2,\dots,5$. Therefore, the minimum number of operations required is $1$.
For the third test case, performing the operation with $k=4$ followed by $k=3$ results in $P$ changing as $(3,2,1,7,5,6,4) \rightarrow (1,2,3,7,4,5,6) \rightarrow (1,2,3,4,5,6,7)$.
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。