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