Codeforces Global Round 21
G
Fishingprince Plays With Array Again
Codeforces
3300
原题
← FH →
翻译中…

Suppose you are given a 1-indexed sequence $a$ of non-negative integers, whose length is $n$, and two integers $x$, $y$. In consecutive $t$ seconds ($t$ can be any positive real number), you can do one of the following operations:

翻译中…
  • Select $1\le i \lt n$, decrease $a_i$ by $x\cdot t$, and decrease $a_{i+1}$ by $y\cdot t$.
  • Select $1\le i \lt n$, decrease $a_i$ by $y\cdot t$, and decrease $a_{i+1}$ by $x\cdot t$.
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Define the minimum amount of time (it might be a real number) required to make all elements in the sequence less than or equal to $0$ as $f(a)$.

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For example, when $x=1$, $y=2$, it takes $3$ seconds to deal with the array $[3,1,1,3]$. We can:

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  • In the first $1.5$ seconds do the second operation with $i=1$.
  • In the next $1.5$ seconds do the first operation with $i=3$.
翻译中…

We can prove that it's not possible to make all elements less than or equal to $0$ in less than $3$ seconds, so $f([3,1,1,3])=3$.

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Now you are given a 1-indexed sequence $b$ of positive integers, whose length is $n$. You are also given positive integers $x$, $y$. Process $q$ queries of the following two types:

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  • 1 k v: change $b_k$ to $v$.
  • 2 l r: print $f([b_l,b_{l+1},\dots,b_r])$.
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Input

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The first line of input contains two integers $n$ and $q$ ($2\le n\le 2\cdot 10^5$, $1\le q\le 2\cdot 10^5$).

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The second line of input contains two integers $x$ and $y$ ($1\le x,y\le 10^6$).

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The third line of input contains $n$ integers $b_1,b_2,\ldots,b_n$ ($1\le b_i\le 10^6$).

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This is followed by $q$ lines. Each of these $q$ lines contains three integers. The first integer $op$ is either $1$ or $2$.

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  • If it is $1$, it is followed by two integers $k$, $v$ ($1\le k\le n$, $1\le v\le 10^6$). It means that you should change $b_k$ to $v$.
  • If it is $2$, it is followed by two integers $l$, $r$ ($1\le l \lt r\le n$). It means that you should print $f([b_l,b_{l+1},\dots,b_r])$.
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Output

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For each query of type $2$, print one real number — the answer to the query. Your answer is considered correct if its absolute error or relative error does not exceed $10^{-9}$.

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Note

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Let's analyse the sample.

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In the first query, we are asked to compute $f([3,1,1,4])$. The answer is $3.5$. One optimal sequence of operations is:

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  • In the first $1.5$ seconds do the second operation with $i=1$.
  • In the next $2$ seconds do the first operation with $i=3$.
翻译中…

In the third query, we are asked to compute $f([1,1,1])$. The answer is $1$. One optimal sequence of operations is:

翻译中…
  • In the first $0.5$ seconds do the second operation with $i=1$.
  • In the next $0.5$ seconds do the first operation with $i=2$.
翻译中…

样例

Input #1
4 3
1 2
3 1 1 4
2 1 4
1 1 1
2 1 3
Output #1
3.500000000000000
1.000000000000000
InputCopy OutputCopy
题目信息
题号
1696G
时间限制
6 s
内存限制
1024 MB
标签
暴力
数据结构
计算几何
数学

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。