AtCoder Grand Contest 014
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Problem Statement
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Takahashi loves sorting.
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He has a permutation $(p_1,p_2,...,p_N)$ of the integers from $1$ through $N$. Now, he will repeat the following operation until the permutation becomes $(1,2,...,N)$:
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- First, we will define high and low elements in the permutation, as follows. The
$i$-th element in the permutation is high if the maximum element between the$1$-st and$i$-th elements, inclusive, is the$i$-th element itself, and otherwise the$i$-th element is low. - Then, let
$a_1,a_2,...,a_k$be the values of the high elements, and$b_1,b_2,...,b_{N-k}$be the values of the low elements in the current permutation, in the order they appear in it. - Lastly, rearrange the permutation into
$(b_1,b_2,...,b_{N-k},a_1,a_2,...,a_k)$.
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How many operations are necessary until the permutation is sorted?
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Constraints
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$1 ≤ N ≤ 2×10^5$$(p_1,p_2,...,p_N)$is a permutation of the integers from$1$through$N$.
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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_2 ... p_N
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Output
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Print the number of operations that are necessary until the permutation is sorted.
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样例
Input #1
5
3 5 1 2 4
Output #1
3
The initial permutation is $(3,5,1,2,4)$, and each operation changes it as follows:
- In the first operation, the $1$-st and $2$-nd elements are high, and the $3$-rd, $4$-th and $5$-th are low. The permutation becomes: $(1,2,4,3,5)$.
- In the second operation, the $1$-st, $2$-nd, $3$-rd and $5$-th elements are high, and the $4$-th is low. The permutation becomes: $(3,1,2,4,5)$.
- In the third operation, the $1$-st, $4$-th and $5$-th elements are high, and the $2$-nd and $3$-rd and $5$-th are low. The permutation becomes: $(1,2,3,4,5)$.
Input #2
5
5 4 3 2 1
Output #2
4
Input #3
10
2 10 5 7 3 6 4 9 8 1
Output #3
6
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。