CF461B Appleman and Tree

#include<cstdio>
#define ll long long
#include<algorithm>
using namespace std;
const int N=1e5+10;
const ll mod=1e9+7;
int v[N],h[N],n,p,cnt;
ll dp[N][2];
struct edge{
    int v,nxt;
}e[N<<1];
inline void add(int a,int b)
{
    e[++cnt].v=b;
    e[cnt].nxt=h[a];
    h[a]=cnt;
}
template <typename e> inline void read(e &x)
{
    x=0;int f=1;char ch=getchar();
    while(ch<'0' || ch>'9') {if(ch=='-') f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9') {x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}
    x*=f;
}
void dfs(int u,int fa)
{
    for(int i=h[u];i;i=e[i].nxt)
    {
        int v=e[i].v;
        if(v==fa) continue;
        dfs(v,u);
        dp[u][1]=(dp[u][1]*((dp[v][0]+dp[v][1])%mod)%mod+dp[u][0]*dp[v][1]%mod)%mod;
        dp[u][0]=dp[u][0]*(dp[v][0]+dp[v][1]%mod)%mod;
    }
}
int main()
{
    read(n);register int i;
    for(i=2;i<=n;++i) read(p),++p,add(p,i),add(i,p);
    for(i=1;i<=n;++i) 
    {
        read(v[i]);
        dp[i][v[i]]=1;
    } 
    dfs(1,0);
    printf("%lld",dp[1][1]);
    return 0;
}