codeforces#P1442B. Identify the Operations
Identify the Operations
Description
We start with a permutation $a_1, a_2, \ldots, a_n$ and with an empty array $b$. We apply the following operation $k$ times.
On the $i$-th iteration, we select an index $t_i$ ($1 \le t_i \le n-i+1$), remove $a_{t_i}$ from the array, and append one of the numbers $a_{t_i-1}$ or $a_{t_i+1}$ (if $t_i-1$ or $t_i+1$ are within the array bounds) to the right end of the array $b$. Then we move elements $a_{t_i+1}, \ldots, a_n$ to the left in order to fill in the empty space.
You are given the initial permutation $a_1, a_2, \ldots, a_n$ and the resulting array $b_1, b_2, \ldots, b_k$. All elements of an array $b$ are distinct. Calculate the number of possible sequences of indices $t_1, t_2, \ldots, t_k$ modulo $998\,244\,353$.
Each test contains multiple test cases. The first line contains an integer $t$ ($1 \le t \le 100\,000$), denoting the number of test cases, followed by a description of the test cases.
The first line of each test case contains two integers $n, k$ ($1 \le k < n \le 200\,000$): sizes of arrays $a$ and $b$.
The second line of each test case contains $n$ integers $a_1, a_2, \ldots, a_n$ ($1 \le a_i \le n$): elements of $a$. All elements of $a$ are distinct.
The third line of each test case contains $k$ integers $b_1, b_2, \ldots, b_k$ ($1 \le b_i \le n$): elements of $b$. All elements of $b$ are distinct.
The sum of all $n$ among all test cases is guaranteed to not exceed $200\,000$.
For each test case print one integer: the number of possible sequences modulo $998\,244\,353$.
Input
Each test contains multiple test cases. The first line contains an integer $t$ ($1 \le t \le 100\,000$), denoting the number of test cases, followed by a description of the test cases.
The first line of each test case contains two integers $n, k$ ($1 \le k < n \le 200\,000$): sizes of arrays $a$ and $b$.
The second line of each test case contains $n$ integers $a_1, a_2, \ldots, a_n$ ($1 \le a_i \le n$): elements of $a$. All elements of $a$ are distinct.
The third line of each test case contains $k$ integers $b_1, b_2, \ldots, b_k$ ($1 \le b_i \le n$): elements of $b$. All elements of $b$ are distinct.
The sum of all $n$ among all test cases is guaranteed to not exceed $200\,000$.
Output
For each test case print one integer: the number of possible sequences modulo $998\,244\,353$.
Samples
3
5 3
1 2 3 4 5
3 2 5
4 3
4 3 2 1
4 3 1
7 4
1 4 7 3 6 2 5
3 2 4 5
2
0
4
Note
$\require{cancel}$
Let's denote as $a_1 a_2 \ldots \cancel{a_i} \underline{a_{i+1}} \ldots a_n \rightarrow a_1 a_2 \ldots a_{i-1} a_{i+1} \ldots a_{n-1}$ an operation over an element with index $i$: removal of element $a_i$ from array $a$ and appending element $a_{i+1}$ to array $b$.
In the first example test, the following two options can be used to produce the given array $b$:
- $1 2 \underline{3} \cancel{4} 5 \rightarrow 1 \underline{2} \cancel{3} 5 \rightarrow 1 \cancel{2} \underline{5} \rightarrow 1 2$; $(t_1, t_2, t_3) = (4, 3, 2)$;
- $1 2 \underline{3} \cancel{4} 5 \rightarrow \cancel{1} \underline{2} 3 5 \rightarrow 2 \cancel{3} \underline{5} \rightarrow 1 5$; $(t_1, t_2, t_3) = (4, 1, 2)$.
In the second example test, it is impossible to achieve the given array no matter the operations used. That's because, on the first application, we removed the element next to $4$, namely number $3$, which means that it couldn't be added to array $b$ on the second step.
In the third example test, there are four options to achieve the given array $b$:
- $1 4 \cancel{7} \underline{3} 6 2 5 \rightarrow 1 4 3 \cancel{6} \underline{2} 5 \rightarrow \cancel{1} \underline{4} 3 2 5 \rightarrow 4 3 \cancel{2} \underline{5} \rightarrow 4 3 5$;
- $1 4 \cancel{7} \underline{3} 6 2 5 \rightarrow 1 4 3 \cancel{6} \underline{2} 5 \rightarrow 1 \underline{4} \cancel{3} 2 5 \rightarrow 1 4 \cancel{2} \underline{5} \rightarrow 1 4 5$;
- $1 4 7 \underline{3} \cancel{6} 2 5 \rightarrow 1 4 7 \cancel{3} \underline{2} 5 \rightarrow \cancel{1} \underline{4} 7 2 5 \rightarrow 4 7 \cancel{2} \underline{5} \rightarrow 4 7 5$;
- $1 4 7 \underline{3} \cancel{6} 2 5 \rightarrow 1 4 7 \cancel{3} \underline{2} 5 \rightarrow 1 \underline{4} \cancel{7} 2 5 \rightarrow 1 4 \cancel{2} \underline{5} \rightarrow 1 4 5$;