BZOJ 3167: [Heoi2013]Sao

/**************************************************************
    Problem: 3167
    User: BeiYu
    Language: C++
    Result: Accepted
    Time:8336 ms
    Memory:18580 kb
****************************************************************/
 
#include <bits/stdc++.h>
using namespace std;
 
typedef long long LL;
typedef pair<int,int> pr;
const int N = 1050;
const LL p = 1e9+7;
 
#define mpr make_pair
#define x first
#define y second
 
int T,n;
vector<pr> h[N];
LL fac[N<<1],ifac[N<<1];
LL f[N][N],g[N][N],sz[N],tmp[N];
 
LL Pow(LL a,LL b,LL r=1) { for(;b;b>>=1,a=a*a%p) if(b&1) r=r*a%p;return r; }
void Add(LL &x,LL y) { x=(x+y)%p; }
void init(int n) {
    fac[0]=1;
    for(int i=1;i<=n;i++) fac[i]=fac[i-1]*i%p;
    ifac[n]=Pow(fac[n],p-2),ifac[0]=1;
    for(int i=n-1;i;--i) ifac[i]=ifac[i+1]*(i+1)%p;
}
LL C(int n,int m) { return n<m?0:fac[n]*ifac[m]%p*ifac[n-m]%p; }
void AddEdge(int fr,int to,int v) { h[fr].push_back(mpr(to,v)); }
void clr() {
    memset(f,0,sizeof(f));
    memset(g,0,sizeof(g));
    for(int i=0;i<N;i++) h[i].clear();
}
void DFS(int u,int fa) {
    sz[u]=1,f[u][1]=1;
    for(int t=0,v;t<(int)h[u].size();t++) if((v=h[u][t].x)!=fa){
        DFS(v,u);
        for(int i=0;i<=sz[u]+sz[v];i++) tmp[i]=0;
        if(h[u][t].y) for(int i=1;i<=sz[u];i++) for(int j=1;j<=sz[v];j++) 
            Add(tmp[i+j],f[u][i]*g[v][j]%p*C(i+j-1,j)%p*C(sz[u]+sz[v]-i-j,sz[v]-j)%p);
        else for(int i=1;i<=sz[u];i++) for(int j=0;j<=sz[v];j++) 
            Add(tmp[i+j],f[u][i]*(g[v][sz[v]]-g[v][j]+p)%p*C(i+j-1,j)%p*C(sz[u]+sz[v]-i-j,sz[v]-j)%p);
        sz[u]+=sz[v];
        for(int i=1;i<=sz[u];i++) f[u][i]=tmp[i];
    }
    for(int i=1;i<=sz[u];i++) g[u][i]=(g[u][i-1]+f[u][i])%p;
     
/*  cout<<"------"<<endl;
    cout<<u<<" "<<fa<<" "<<sz[u]<<endl;
    for(int i=1;i<=sz[u];i++) cout<<f[u][i]<<" ";cout<<endl;*/
}
int main() {
    for(scanf("%d",&T),init(2000);T--;) {
        clr();scanf("%d",&n);
        for(int i=1;i<n;i++) {
            int u,v;char opt[5];
            scanf("%d%s%d",&u,opt,&v);
            u++,v++;
            if(opt[0]==‘<‘) AddEdge(u,v,0),AddEdge(v,u,1);
            else AddEdge(u,v,1),AddEdge(v,u,0);
        }DFS(1,1);
        LL ans=0;
        for(int i=1;i<=n;i++) Add(ans,f[1][i]);
        printf("%lld\n",ans);
    }return 0;
}