問題一覧 > 通常問題

No.2874 Gunegune Tree

レベル : / AI推定難易度 : 1100 / 実行時間制限 : 1ケース 2.000秒 / メモリ制限 : 512 MB / 標準ジャッジ問題
タグ : (AC するまで非表示) / 解いたユーザー数 68
作問者 : 寝癖 / テスター : yuusaan 👑 seekworser
お気に入りにしたユーザー ProblemId : 11180 / 自分の提出
問題文最終更新日: 2024-08-29 19:19:39
This statement was translated by AI (claude-opus-5-5, effort medium) and may contain errors or differ in nuance from the original. The original statement takes precedence. Back to the original
yukicoder contest 444 (順位表) の他の問題:

Problem Statement

Neguse-kun has bought the seed of a mysterious plant. He is going to grow it at his home starting today.

Let today be day $0$. Each time $1$ day passes, this plant grows according to the following rules.

  • On day $0$, the tip of the plant is at the origin $(0,0)$ of a $2$-dimensional plane.
  • If the coordinates of the tip of the plant on day $i\ (\ge0)$ are $(x,y)$, then the coordinates of the tip on day $i+1$ are one of $(x+1,y),(x+1,y+1),(x,y+1),(x-1,y+1),(x-1,y)$. That is, it grows in one of the following directions: right, upper right, up, upper left, or left.
  • Let $P_i,P_{i+1},P_{i+2}$ be the positions of the tip of the plant on days $i,i+1,i+2$. Then $\angle P_iP_{i+1}P_{i+2}>90^\circ$ holds. That is, the plant never bends at an acute or right angle.
  • The direction of growth is chosen independently and uniformly at random from all possible directions.

Neguse-kun is troubled by the low ceiling of his home, and he is very concerned about how tall this plant will grow.

Find the expected value of the height of the plant (that is, the $y$-coordinate of its tip) on day $N$ after he starts growing it, modulo ${\rm mod}\ 998244353$.

What is an expected value ${\rm mod}\ 998244353$?

It can be proved that the expected value to be found is always a rational number. Moreover, under the constraints of this problem, it is guaranteed that when the expected value is expressed as an irreducible fraction $\frac{p}{q}$, $q$ is not divisible by $998244353$. In this case, there exists a unique $0\le r < 998244353$ satisfying $p=qr\ ({\rm mod}\ 998244353)$, so output this $r$.

Input

$N$
  • $1\le N\le 2\times 10^5$
  • $N$ is an integer.

Output

Output the expected value of the height of the plant on day $N$, ${\rm mod}\ 998244353$, on a single line.

Sample

Sample 1
Input
1
Output
798595483

On day $1$, the plant grows in one of $5$ directions with equal probability.

If it grows to the upper right, up, or to the upper left, the height becomes $1$, and if it grows to the right or left, the height becomes $0$. Therefore, the expected value to be found is $1\times\frac35+0\times\frac25 = \frac35$.

Sample 2
Input
2
Output
465847366
Sample 3
Input
3
Output
277290100

提出するには、Twitter 、GitHub、 Googleもしくは右上の雲マークをクリックしてアカウントを作成してください。