6317: ABC231 —— G - Balls in Boxes
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Description
We have $N$ boxes numbered $1$ to $N$. Initially, Box $i$ contains $A_i$ balls.
You will repeat the following operation $K$ times.
Find the expected value of the score modulo $998244353$.
You will repeat the following operation $K$ times.
- Choose one box out of the $N$ uniformly at random (each time independently). Add one ball to the chosen box.
Find the expected value of the score modulo $998244353$.
Notes
When the expected value in question is represented as an irreducible fraction $p/q$, there uniquely exists an integer $r$ such that $rq\equiv p \pmod{998244353}$ and $0\leq r < 998244353$ under the Constraints of this problem. This $r$ is the value we seek.Input
Input is given from Standard Input in the following format:
$N\ K$
$A_1\ \ldots\ A_N$
$N\ K$
$A_1\ \ldots\ A_N$
Output
Print the answer.
Constraints
$1≤N≤1000$
$1 \leq K \leq 10^9$
$0 \leq A_i \leq 10^9$
$1 \leq K \leq 10^9$
$0 \leq A_i \leq 10^9$
Sample 1 Input
3 1
1 2 3
Sample 1 Output
665496245
After the operation, the score will be as follows.
- When choosing Box $1$ in the operation, $2\times 2\times 3=12$.
- When choosing Box $2$ in the operation, $1\times 3\times 3=9$.
- When choosing Box $3$ in the operation, 1\times 2\times 4=8$.
Sample 2 Input
2 2
1 2
Sample 2 Output
499122182
After the operations, the score will be as follows.
- When choosing Box $1$ in the first operation and Box $1$ in the second, $3\times 2=6$.
- When choosing Box $1$ in the first operation and Box $2$ in the second, $2\times 3=6$.
- When choosing Box $2$ in the first operation and Box $1$ in the second, $2\times 3=6$.
- When choosing Box $2$ in the first operation and Box $2$ in the second, $1\times 4=4$.
Sample 3 Input
10 1000000000
998244350 998244351 998244352 998244353 998244354 998244355 998244356 998244357 998244358 998244359
Sample 3 Output
138512322