Codeforces Round 641 (Div. 1)
D
Slime and Biscuits
Codeforces
3200
原题
← CE →
翻译中…

Slime and his $n$ friends are at a party. Slime has designed a game for his friends to play.

翻译中…

At the beginning of the game, the $i$-th player has $a_i$ biscuits. At each second, Slime will choose a biscuit randomly uniformly among all $a_1 + a_2 + \ldots + a_n$ biscuits, and the owner of this biscuit will give it to a random uniform player among $n-1$ players except himself. The game stops when one person will have all the biscuits.

翻译中…

As the host of the party, Slime wants to know the expected value of the time that the game will last, to hold the next activity on time.

翻译中…

For convenience, as the answer can be represented as a rational number $\frac{p}{q}$ for coprime $p$ and $q$, you need to find the value of $(p \cdot q^{-1})\mod 998\,244\,353$. You can prove that $q\mod 998\,244\,353 \neq 0$.

翻译中…

Input

翻译中…

The first line contains one integer $n\ (2\le n\le 100\,000)$: the number of people playing the game.

翻译中…

The second line contains $n$ non-negative integers $a_1,a_2,\dots,a_n\ (1\le a_1+a_2+\dots+a_n\le 300\,000)$, where $a_i$ represents the number of biscuits the $i$-th person own at the beginning.

翻译中…

Output

翻译中…

Print one integer: the expected value of the time that the game will last, modulo $998\,244\,353$.

翻译中…

Note

翻译中…

For the first example, in the first second, the probability that player $1$ will give the player $2$ a biscuit is $\frac{1}{2}$, and the probability that player $2$ will give the player $1$ a biscuit is $\frac{1}{2}$. But anyway, the game will stop after exactly $1$ second because only one player will occupy all biscuits after $1$ second, so the answer is $1$.

翻译中…

样例

Input #1
2
1 1
Output #1
1
InputCopy OutputCopy
Input #2
2
1 2
Output #2
3
InputCopy OutputCopy
Input #3
5
0 0 0 0 35
Output #3
0
InputCopy OutputCopy
Input #4
5
8 4 2 0 1
Output #4
801604029
InputCopy OutputCopy
题目信息
题号
1349D
时间限制
2 s
内存限制
256 MB
标签
数学
概率论

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