Felicity is Coming!
题意翻译
神奇宝贝的进化方案是一个全排列，假设有三种宝可梦，那么对应就可以有：$(1,2,3)$，$(1,3,2)$，$(2,1,3)$，$(2,3,1)$，$(3,1,2)$，$(3,2,1)$ 这六种进化方案（六种全排列）。
这里 $(1,3,2)$ 相当于：$1$ 进化成 $1$，$2$ 进化成 $3$，$3$ 进化成 $2$。需要满足所有约束条件才能作为可行进化方案：
对于一个训练馆，之前有 $a$ 个 $b$ 种类的宝可梦，那么训练馆里所有的宝可梦进化之后，还要有 $a$ 个 $b$ 种类的宝可梦才行，种类不能增加，不能减少，也不能改变。
问一共有多少个可行方案。
题目描述
It's that time of the year, Felicity is around the corner and you can see people celebrating all around the Himalayan region. The Himalayan region has $ n $ gyms. The $ i $ -th gym has $ g_{i} $ Pokemon in it. There are $ m $ distinct Pokemon types in the Himalayan region numbered from $ 1 $ to $ m $ . There is a special evolution camp set up in the fest which claims to evolve any Pokemon. The type of a Pokemon could change after evolving, subject to the constraint that if two Pokemon have the same type before evolving, they will have the same type after evolving. Also, if two Pokemon have different types before evolving, they will have different types after evolving. It is also possible that a Pokemon has the same type before and after evolving.
Formally, an evolution plan is a permutation $ f $ of $ {1,2,...,m} $ , such that $ f(x)=y $ means that a Pokemon of type $ x $ evolves into a Pokemon of type $ y $ .
The gym leaders are intrigued by the special evolution camp and all of them plan to evolve their Pokemons. The protocol of the mountain states that in each gym, for every type of Pokemon, the number of Pokemon of that type before evolving any Pokemon should be equal the number of Pokemon of that type after evolving all the Pokemons according to the evolution plan. They now want to find out how many distinct evolution plans exist which satisfy the protocol.
Two evolution plans $ f_{1} $ and $ f_{2} $ are distinct, if they have at least one Pokemon type evolving into a different Pokemon type in the two plans, i. e. there exists an $ i $ such that $ f_{1}(i)≠f_{2}(i) $ .
Your task is to find how many distinct evolution plans are possible such that if all Pokemon in all the gyms are evolved, the number of Pokemon of each type in each of the gyms remains the same. As the answer can be large, output it modulo $ 10^{9}+7 $ .
输入输出格式
输入格式
The first line contains two integers $ n $ and $ m $ ( $ 1<=n<=10^{5} $ , $ 1<=m<=10^{6} $ ) — the number of gyms and the number of Pokemon types.
The next $ n $ lines contain the description of Pokemons in the gyms. The $ i $ -th of these lines begins with the integer $ g_{i} $ ( $ 1<=g_{i}<=10^{5} $ ) — the number of Pokemon in the $ i $ -th gym. After that $ g_{i} $ integers follow, denoting types of the Pokemons in the $ i $ -th gym. Each of these integers is between $ 1 $ and $ m $ .
The total number of Pokemons (the sum of all $ g_{i} $ ) does not exceed $ 5·10^{5} $ .
输出格式
Output the number of valid evolution plans modulo $ 10^{9}+7 $ .
输入输出样例
输入样例 #1
2 3
2 1 2
2 2 3
输出样例 #1
1
输入样例 #2
1 3
3 1 2 3
输出样例 #2
6
输入样例 #3
2 4
2 1 2
3 2 3 4
输出样例 #3
2
输入样例 #4
2 2
3 2 2 1
2 1 2
输出样例 #4
1
输入样例 #5
3 7
2 1 2
2 3 4
3 5 6 7
输出样例 #5
24
说明
In the first case, the only possible evolution plan is:
In the second case, any permutation of $ (1,2,3) $ is valid.
In the third case, there are two possible plans:
 In the fourth case, the only possible evolution plan is:
