Codeforces Round 777 (Div. 2)
F
Madoka and Laziness
Codeforces
3100
原题
← E→
翻译中…

Madoka has become too lazy to write a legend, so let's go straight to the formal description of the problem.

翻译中…

An array of integers $a_1, a_2, \ldots, a_n$ is called a hill if it is not empty and there is an index $i$ in it, for which the following is true: $a_1 \lt a_2 \lt \ldots \lt a_i \gt a_{i + 1} \gt a_{i + 2} \gt \ldots \gt a_n$.

翻译中…

A sequence $x$ is a subsequence of a sequence $y$ if $x$ can be obtained from $y$ by deletion of several (possibly, zero or all) elements keeping the order of the other elements. For example, for an array $[69, 1000, 228, -7]$ the array $[1000, -7]$ is a subsequence, while $[1]$ and $[-7, 1000]$ are not.

翻译中…

Splitting an array into two subsequences is called good if each element belongs to exactly one subsequence, and also each of these subsequences is a hill.

翻译中…

You are given an array of distinct positive integers $a_1, a_2, \ldots a_n$. It is required to find the number of different pairs of maxima of the first and second subsequences among all good splits. Two pairs that only differ in the order of elements are considered same.

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Input

翻译中…

The first line of input contains a single integer $n$ ($2 \le n \le 5 \cdot 10^5$) — array size.

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The second line of input contains $n$ integers $a_1, a_2, \dots, a_n$ ($1 \le a_i \le 10^9$) — the elements of the array. It is guaranteed that all $a_i$ are pairwise distinct.

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Output

翻译中…

In a single line, print exactly one number — the number of different pairs of maxima of the first and second subsequences among all good splits.

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Note

翻译中…

In the first test case there are 3 possible pairs: $(3, 4)$, $(2, 4)$, $(1, 4)$. And they are achieved with the following partitions: $[1, 2, 3], [4]$; $[4, 3], [1, 2]$; $[1], [2, 4, 3]$

翻译中…

样例

Input #1
4
1 2 4 3
Output #1
3
InputCopy OutputCopy
Input #2
8
2 12 13 7 14 6 11 8
Output #2
4
InputCopy OutputCopy
Input #3
7
9 5 3 10 2 6 8
Output #3
0
InputCopy OutputCopy
Input #4
8
8 6 10 9 1 5 2 14
Output #4
0
InputCopy OutputCopy
题目信息
题号
1647F
时间限制
2 s
内存限制
256 MB
标签
动态规划
贪心

题面与样例版权归 Codeforces 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。