Palindrome-less Arrays

2000ms

262144K

Description:

Let's denote that some array $$$b$$$ is bad if it contains a subarray $$$b_l, b_{l+1}, \dots, b_{r}$$$ of odd length more than $$$1$$$ ($$$l < r$$$ and $$$r - l + 1$$$ is odd) such that $$$\forall i \in \{0, 1, \dots, r - l\}$$$ $$$b_{l + i} = b_{r - i}$$$.

If an array is not bad, it is good.

Now you are given an array $$$a_1, a_2, \dots, a_n$$$. Some elements are replaced by $$$-1$$$. Calculate the number of good arrays you can obtain by replacing each $$$-1$$$ with some integer from $$$1$$$ to $$$k$$$.

Since the answer can be large, print it modulo $$$998244353$$$.

Input:

The first line contains two integers $$$n$$$ and $$$k$$$ ($$$2 \le n, k \le 2 \cdot 10^5$$$) — the length of array $$$a$$$ and the size of "alphabet", i. e., the upper bound on the numbers you may use to replace $$$-1$$$.

The second line contains $$$n$$$ integers $$$a_1, a_2, \dots, a_n$$$ ($$$a_i = -1$$$ or $$$1 \le a_i \le k$$$) — the array $$$a$$$.

Output:

Print one integer — the number of good arrays you can get, modulo $$$998244353$$$.

Sample Input:

2 3
-1 -1

Sample Output:

Sample Input:

5 2
1 -1 -1 1 2

Sample Output:

Sample Input:

5 3
1 -1 -1 1 2

Sample Output:

Sample Input:

4 200000
-1 -1 12345 -1

Sample Output:

735945883

Informação

Provedor Codeforces

Código CF1140E