Gym 102012G Rikka with Intersections of Paths （樹上差分+LCA）

#include<bits/stdc++.h>
using namespace std;
#define debug cout<<"YES\n";
#define rep(x,y,z) for(int (x)=(y);(x)<(z);(x)++)
#define ll long long
#define lrt int l,int r,int rt
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define root l,r,rt
#define mst(a,b) memset((a),(b),sizeof(a))
#define pii pair<int,int>
#define fi first                                  
#define se second
#define mk(x,y) make_pair(x,y)
const int mod=1e9+7;
const int maxn=3e5+100;
const int lz=0;
const ll INF=1e18;
ll powmod(ll x,ll y){ll t; for(t=1;y;y>>=1,x=x*x%mod) if(y&1) t=t*x%mod; return t;}
ll gcd(ll x,ll y){if(y==0) return x;return gcd(y,x%y);}
int n,m,k;
vector<int> g[maxn];
ll fac[maxn],inv[maxn];
ll C(int x,int y){
    if(x<y) return 0;
    return fac[x]*inv[y]%mod*inv[x-y]%mod;
}
int dep[maxn],fa[maxn][20],cnt[maxn],cnt2[maxn];
void dfs1(int u,int f){
    dep[u]=dep[f]+1;
    fa[u][0]=f;rep(i,1,20) fa[u][i]=fa[fa[u][i-1]][i-1];
    rep(i,0,g[u].size()) if(g[u][i]!=f)
        dfs1(g[u][i],u);
}
void dfs2(int u,int f){
    rep(i,0,g[u].size()) if(g[u][i]!=f){
        dfs2(g[u][i],u);
        cnt[u]+=cnt[g[u][i]];
    }
}
int LCA(int x,int y){
    if(dep[x]<dep[y]) swap(x,y);
    int i,j;
    for(i=0;dep[x]>=(1<<i);i++);i--;
    for(int j=i;j>=0;j--) if(dep[x]-(1<<j)>=dep[y])
        x=fa[x][j];
    if(x==y) return x;
    for(int j=i;j>=0;j--) if(fa[x][j]^fa[y][j])
        x=fa[x][j],y=fa[y][j];
    return fa[x][0];
}
int main(){
    ios::sync_with_stdio(false);/*
    freopen("d://in.txt","r",stdin);
    freopen("d://out.txt","w",stdout);*/
    fac[0]=1;rep(i,1,maxn) fac[i]=fac[i-1]*i%mod;
    inv[maxn-1]=powmod(fac[maxn-1],mod-2);
    for(int i=maxn-2;i>=0;i--) inv[i]=inv[i+1]*(i+1)%mod;
    int t;cin>>t;
    ///預處理組合階乘逆元
    while(t--){
        cin>>n>>m>>k;
        mst(cnt,0),mst(cnt2,0);
        rep(i,1,n+1) g[i].clear();
        rep(i,1,n){
            int x,y;
            cin>>x>>y;
            g[x].push_back(y);
            g[y].push_back(x);
        }
        dfs1(1,0);
        rep(i,0,m){
            int x,y,z;
            cin>>x>>y;
            z=LCA(x,y);
            cnt[z]--,cnt[fa[z][0]]--;
            cnt[x]++,cnt[y]++;
            cnt2[z]++;
        }
        dfs2(1,0);
        ///cout<<cnt[1]<<" "<<cnt[2]<<" "<<cnt[3]<<endl;
        ///cout<<cnt2[1]<<" "<<cnt2[2]<<" "<<cnt2[3]<<endl;
        ll ans=0;
        rep(i,1,n+1){
            ans+=(C(cnt[i],k)-C(cnt[i]-cnt2[i],k)+mod)%mod;
            ans%=mod;
        }
        cout<<ans<<"\n";
    }
    return 0;
}