Codeforces Round #568 (Div. 2) G2. Playlist for Polycarp (hard version)

因为不会打公式，随意就先将就一下？

#include<cstdio>
#include<algorithm>
#include<iostream>
#include<cstring>
#include<vector>
using namespace std;
typedef long long LL;
const int N=55;
const int MOD=1e9+7;
int add (int x,int y)   {x=x+y;return x>=MOD?x-MOD:x;}
int mul (int x,int y)   {return (LL)x*y%MOD;}
int dec (int x,int y)   {x=x-y;return x<0?x+MOD:x;}
int Pow (int x,int y)
{if (y==0) return 1;if (y==1) return x;int lalal=Pow(x,y>>1);lalal=mul(lalal,lalal);if (y&1) lalal=mul(lalal,x);return lalal;
}
int n,m;
int g[N][N][N][4];
int h[N][N][N];
int JC[N];
void Init (int n)
{memset(g,0,sizeof(g));g[0][0][1][2]=1;g[0][1][0][1]=1;g[1][0][0][0]=1;JC[0]=1;for (int u=1;u<=n;u++) JC[u]=mul(JC[u-1],u);for (int u=0;u<=n;u++)for (int i=0;i<=n;i++)for (int j=0;j<=n;j++) for (int k=0;k<=2;k++)    if (g[u][i][j][k]){if (k!=0) g[u+1][i][j][0]=add(g[u+1][i][j][0],g[u][i][j][k]);if (k!=1) g[u][i+1][j][1]=add(g[u][i+1][j][1],g[u][i][j][k]);if (k!=2) g[u][i][j+1][2]=add(g[u][i][j+1][2],g[u][i][j][k]);int now=mul(mul(mul(JC[u],JC[i]),JC[j]),g[u][i][j][k]);//if (u==2&&i==1&&j==0) printf("%d %d\n",g[u][i][j][k],(mul(JC[u],JC[i]),JC[j]));h[u][i][j]=add(h[u][i][j],now);}//printf("%d\n",h[2][1][0]);
}
vector<int> vec[N];
int f[3][N][2505];
int sum[3];
int d[N][N][2505];
int main()
{Init(50);scanf("%d%d",&n,&m);for (int u=1;u<=n;u++){int t,g;scanf("%d%d",&t,&g);sum[g-1]+=t;vec[g-1].push_back(t);}if (sum[0]>sum[2])    {swap(sum[0],sum[2]);swap(vec[0],vec[2]);}if (sum[1]>sum[2])    {swap(sum[1],sum[2]);swap(vec[1],vec[2]);}for (int u=0;u<=2;u++){int siz=vec[u].size();f[u][0][0]=1;for (int i=0;i<siz;i++)for (int j=i+1;j>=1;j--)for (int k=sum[u];k>=vec[u][i];k--)f[u][j][k]=add(f[u][j][k],f[u][j-1][k-vec[u][i]]);}for (int u=0;u<=vec[0].size();u++)for (int j=0;j<=sum[0];j++) if (f[0][u][j])for (int i=0;i<=vec[1].size();i++)for (int k=0;k<=sum[1];k++) if (f[1][i][k])d[u][i][j+k]=add(d[u][i][j+k],mul(f[0][u][j],f[1][i][k]));int ans=0;for (int u=0;u<=vec[2].size();u++)for (int i=0;i<=sum[2];i++) if (f[2][u][i]){int t=m-i;for (int j=0;j<=vec[0].size();j++)for (int k=0;k<=vec[1].size();k++)ans=add(ans,mul(h[u][j][k],(mul(d[j][k][t],f[2][u][i]))));}printf("%d\n",ans);return 0;
}