P23292 [AtCoder] Lottery
提高
题目描述

Problem Statement

Takahashi is participating in a lottery.
Each time he takes a draw, he gets one of the N prizes available. Prize i is awarded with probability $\frac{W_i}{\sum_{j=1}^{N}W_j}$. The results of the draws are independent of each other.
What is the probability that he gets exactly M different prizes from K draws? Find it modulo 998244353.

Input

Input is given from Standard Input in the following format:
N M K
W_1
$\vdots$
W_N

Output

Print the answer.

Constraints

  • $1 \leq K \leq 50$
  • $1 \leq M \leq N \leq 50$
  • 0 < W_i
  • $0 < W_1 + \ldots + W_N < 998244353$
  • All values in input are integers.

Sample Input 1

2 1 2
2
1

Sample Output 1

221832079

Each draw awards Prize 1 with probability $\frac{2}{3}$ and Prize 2 with probability $\frac{1}{3}$.
He gets Prize 1 at both of the two draws with probability $\frac{4}{9}$, and Prize 2 at both draws with probability $\frac{1}{9}$, so the sought probability is $\frac{5}{9}$.
The modulo 998244353 representation of this value, according to Note, is 221832079.

Sample Input 2

3 3 2
1
1
1

Sample Output 2

0

It is impossible to get three different prizes from two draws, so the sought probability is 0.

Sample Input 3

3 3 10
499122176
499122175
1

Sample Output 3

335346748

Sample Input 4

10 8 15
1
1
1
1
1
1
1
1
1
1

Sample Output 4

755239064

输入格式

见题面 Input 部分

输出格式

见题面 Output 部分

样例输入
2 1 2 2 1
样例输出
221832079