AtCoder Regular Contest 132
E
Paw
AtCoder
⌀ 3144
原题
← DF →
翻译中…

Problem Statement

翻译中…

There are $n$ squares arranged in a row. Each square has a left- or right-pointing footprint or a hole. The initial state of each square is described by a string $s$ consisting of ., <, >. If the $i$-th character of $s$ is ., the $i$-th square from the left has a hole; if that character is <, that square has a left-pointing footprint; if that character is >, that square has a right-pointing footprint.

翻译中…

Snuke, the cat, will repeat the following procedure until there is no more square with a hole.

翻译中…
  • Step $1$: Choose one square with a hole randomly with equal probability.
  • Step $2$: Fill the hole in the chosen square, stand there, and face to the left or right randomly with equal probability.
  • Step $3$: Keep walking in the direction Snuke is facing until he steps on a square with a hole or exits the row of squares.
翻译中…

Here, the choices of squares and directions are independent of each other.

翻译中…

When Snuke walks on a square (without a hole), that square gets a footprint in the direction he walks in. If the square already has a footprint, it gets erased and replaced by a new one. For example, in the situation >.<><.><, if Snuke chooses the $6$-th square from the left and faces to the left, the $6$-th, $5$-th, $4$-th, $3$-rd squares get left-pointing footprints: >.<<<<><.

翻译中…

Find the expected value of the number of left-pointing footprints when Snuke finishes the procedures, modulo $998244353$.

翻译中…

Note

翻译中…

When the sought expected value is represented as an irreducible fraction $p/q$, there uniquely exists an integer $r$ such that $rq\equiv p ~(\text{mod } 998244353)$ and $0 \leq r \lt 998244353$ under the Constraints of this problem. This $r$ is the value to be found.

翻译中…

Constraints

翻译中…
  • $1 \leq n \leq 10^5$
  • $s$ is a string of length $n$ consisting of ., <, >.
  • $s$ contains at least one ..
翻译中…

Input

翻译中…

Input is given from Standard Input in the following format:

翻译中…

n
s

翻译中…

Output

翻译中…

Print the expected value of the number of left-pointing footprints, modulo $998244353$.

翻译中…

样例

Input #1
5
><.<<
Output #1
3
In Step $1$, Snuke always chooses the only square with a hole. If Snuke faces to the left in Step $2$, the squares become `<<<<<`, where $5$ squares have left-pointing footprints. If Snuke faces to the right in Step $2$, the squares become `><>>>`, where $1$ square has a left-pointing footprint. Therefore, the answer is $\frac{5+1}{2}=3$.
Input #2
20
>.>.<>.<<.<>.<..<>><
Output #2
848117770
题目信息
题号
arc132_e
时间限制
2 s
内存限制
1024 MB

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。