G. The Galactic Olympics

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本文链接： https://blog.csdn.net/weixin_39132605/article/details/100587910

http://codeforces.com/gym/101147/problem/G 

总结：第二类斯特林数变形；

n个球放进k个有差别盒子；就是放进k个无差别得*i；

dp[i][j]表示把j个元素分成i个集合； 

#include <iostream>
#include <cstring>
#include <queue>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <set>
#include <map>
#include <stack>
//#include <tr1/unordered_map>
//#include <unordered_map>
#include <cmath>
//#include<bits/stdc++.h>
using namespace std;

#define sfi(i) scanf("%d",&i)
#define sfl(i) scanf("%I64d",&i)
#define sfs(i) scanf("%s",(i))
#define pri(i) printf("%d\n",i)
#define prl(i) printf("%I64d\n",i)
#define sff(i) scanf("%lf",&i)
#define ll long long
#define ull unsigned long long
#define uint unsigned int
#define mem(x,y) memset(x,y,sizeof(x))
#define INF 0x3f3f3f3f
#define inf 1e18
#define eps 1e-10
#define PI acos(-1.0)
#define lowbit(x) ((x)&(-x))
#define fl() printf("flag\n")
#define MOD(x) ((x%mod)+mod)%mod
#define endl '\n'
#define pb push_back
#define lson (rt<<1)
#define rson (rt<<1|1)
#define FAST_IO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)

template<typename T>inline void read(T &x)
{
    x=0;
    static int p;p=1;
    static char c;c=getchar();
    while(!isdigit(c)){if(c=='-')p=-1;c=getchar();}
    while(isdigit(c)) {x=(x<<1)+(x<<3)+(c-48);c=getchar();}
    x*=p;
}

//-----------------------------------------------

const int maxn=1e3+9;
const int maxm=3e6+9;
const int mod=1e9+7;

ll dp[maxn][maxn];

int main()
{
    FAST_IO;
    //freopen("input.txt","r",stdin);



    freopen("galactic.in","r",stdin);

    for(int i=1;i<=1000;i++)
    {
        for(int j=1;j<=i;j++)
        {
            if(j==1) dp[i][1]=1;
            else if(i==j) dp[i][j]=dp[i-1][j-1]*i%mod;
            else dp[i][j]=(dp[i-1][j-1]+dp[i-1][j])*j%mod;
        }
    }
    int T;
    //sfi(T);
    cin>>T;
    while(T--)
    {
        int n,k;
        cin>>n>>k;
        if(k>n) cout<<0<<endl;
        else cout<<dp[n][k]<<endl;
    }

    return 0;
}