AtCoder Beginner Contest 130
E
Common Subsequence
AtCoder
⌀ 1676
原题
← DF →
翻译中…

Problem Statement

翻译中…

You are given two integer sequences $S$ and $T$ of length $N$ and $M$, respectively, both consisting of integers between $1$ and $10^5$ (inclusive).

翻译中…

In how many pairs of a subsequence of $S$ and a subsequence of $T$ do the two subsequences are the same in content?

翻译中…

Here the subsequence of $A$ is a sequence obtained by removing zero or more elements from $A$ and concatenating the remaining elements without changing the order.

翻译中…

For both $S$ and $T$, we distinguish two subsequences if the sets of the indices of the removed elements are different, even if the subsequences are the same in content.

翻译中…

Since the answer can be tremendous, print the number modulo $10^9+7$.

翻译中…

Constraints

翻译中…
  • $1 \leq N, M \leq 2 \times 10^3$
  • The length of $S$ is $N$.
  • The length of $T$ is $M$.
  • $1 \leq S_i, T_i \leq 10^5$
  • All values in input are integers.
翻译中…

Input

翻译中…

Input is given from Standard Input in the following format:

翻译中…

N M
S_1 S_2 ... S_{N-1} S_{N}
T_1 T_2 ... T_{M-1} T_{M}

翻译中…

Output

翻译中…

Print the number of pairs of a subsequence of $S$ and a subsequence of $T$ such that the subsequences are the same in content, modulo $10^9+7$.

翻译中…

样例

Input #1
2 2
1 3
3 1
Output #1
3
$S$ has four subsequences: $(), (1), (3), (1, 3)$. $T$ has four subsequences: $(), (3), (1), (3, 1)$. There are $1 \times 1$ pair of subsequences in which the subsequences are both $()$, $1 \times 1$ pair of subsequences in which the subsequences are both $(1)$, and $1 \times 1$ pair of subsequences in which the subsequences are both $(3)$, for a total of three pairs.
Input #2
2 2
1 1
1 1
Output #2
6
$S$ has four subsequences: $(), (1), (1), (1, 1)$. $T$ has four subsequences: $(), (1), (1), (1, 1)$. There are $1 \times 1$ pair of subsequences in which the subsequences are both $()$, $2 \times 2$ pairs of subsequences in which the subsequences are both $(1)$, and $1 \times 1$ pair of subsequences in which the subsequences are both $(1,1)$, for a total of six pairs. Note again that we distinguish two subsequences if the sets of the indices of the removed elements are different, even if the subsequences are the same in content.
Input #3
4 4
3 4 5 6
3 4 5 6
Output #3
16
Input #4
10 9
9 6 5 7 5 9 8 5 6 7
8 6 8 5 5 7 9 9 7
Output #4
191
Input #5
20 20
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
Output #5
846527861
Be sure to print the number modulo $10^9+7$.
题目信息
题号
abc130_e
时间限制
2 s
内存限制
1024 MB

题面与样例版权归 AtCoder 及出题人所有;中文翻译由 AI 生成(CI 管线),如有出入请以原文为准。