题解 数据恢复

#include <bits/stdc++.h>
using namespace std;
#define INF 0x3f3f3f3f
#define N 300010
#define ll long long
#define fir first
#define sec second
#define make make_pair
#define pb push_back
//#define int long long

char buf[1<<21], *p1=buf, *p2=buf;
#define getchar() (p1==p2&&(p2=(p1=buf)+fread(buf, 1, 1<<21, stdin)), p1==p2?EOF:*p1++)
inline int read() {
	int ans=0, f=1; char c=getchar();
	while (!isdigit(c)) {if (c=='-') f=-f; c=getchar();}
	while (isdigit(c)) {ans=(ans<<3)+(ans<<1)+(c^48); c=getchar();}
	return ans*f;
}

int n;
int head[N], size;
ll a[N], b[N];
struct edge{int to, next;}e[N<<1];
inline void add(int s, int t) {e[++size].to=t; e[size].next=head[s]; head[s]=size;}

namespace force{
	ll ans;
	int p[N], fa[N], back[N];
	void solve() {
		for (int i=2; i<=n; ++i) fa[i]=read();
		for (int i=1; i<=n; ++i) a[i]=read(), b[i]=read();
		for (int i=1; i<=n; ++i) p[i]=i;
		do {
			ll sum=0;
			for (int i=1; i<=n; ++i) back[p[i]]=i;
			for (int i=2; i<=n; ++i) if (back[fa[i]]>back[i]) goto jump;
			for (int i=1; i<=n; ++i) {
				for (int j=i+1; j<=n; ++j) {
					sum+=b[p[i]]*a[p[j]];
				}
			}
			ans=max(ans, sum);
			jump: ;
		} while (next_permutation(p+1, p+n+1));
		printf("%lld\n", ans);
		exit(0);
	}
}

namespace task1{
	priority_queue<pair<double, int>> q;
	int sta[N], top;
	ll suf[N];
	void solve() {
		memset(head, -1, sizeof(head));
		for (int i=2; i<=n; ++i) add(read(), i);
		for (int i=1; i<=n; ++i) a[i]=read(), b[i]=read();
		q.push(make(-1.0*a[1]/b[1], 1));
		pair<double, int> u;
		while (q.size()) {
			u=q.top(); q.pop();
			sta[++top]=u.sec;
			for (int i=head[u.sec],v; ~i; i=e[i].next) {
				v = e[i].to;
				q.push(make(-1.0*a[v]/b[v], v));
			}
		}
		ll ans=0;
		for (int i=n; i; --i) suf[i]=suf[i+1]+a[sta[i]];
		for (int i=1; i<=n; ++i) ans+=b[sta[i]]*suf[i+1];
		// cout<<"sta: "; for (int i=1; i<=top; ++i) cout<<sta[i]<<' '; cout<<endl;
		printf("%lld\n", ans);
		exit(0);
	}
}

namespace task2{
	int p[N], fa[N]; ll ans;
	bool vis[N];
	void check() {
		ll sum=0;
		for (int i=1; i<=n; ++i) {
			for (int j=i+1; j<=n; ++j) {
				sum+=b[p[i]]*a[p[j]];
			}
		}
		ans=max(ans, sum);
	}
	void dfs(int u) {
		if (u>n) {check(); return ;}
		for (int i=1; i<=n; ++i) if (!vis[i] && vis[fa[i]]) {
			vis[i]=1; p[u]=i;
			dfs(u+1);
			vis[i]=0;
		}
	}
	void solve() {
		for (int i=2; i<=n; ++i) fa[i]=read();
		for (int i=1; i<=n; ++i) a[i]=read(), b[i]=read();
		vis[1]=1; p[1]=1;
		dfs(2);
		printf("%lld\n", ans);
		exit(0);
	}
}

namespace task{
	priority_queue<pair<double, int>> q;
	list<int> inc[N];
	int fa[N], f[N], sta[N], stop, siz[N], top[N];
	ll a[N], b[N], a2[N], b2[N], suf[N];
	bool vis[N];
	inline int find(int p) {return fa[p]==p?p:fa[p]=find(fa[p]);}
	inline void uni(int x, int y) {
		// cout<<"uni: "<<x<<' '<<y<<endl;
		int ttop=top[x];
		// for (auto it:inc[y]) inc[x].pb(it);
		inc[x].splice(inc[x].end(), inc[y]);
		siz[x]+=siz[y]; fa[y]=x;
		a[x]=(a[x]+a[y]); b[x]=(b[x]+b[y]);
		top[x]=ttop;
	}
	void solve() {
		for (int i=2; i<=n; ++i) top[i]=f[i]=read();
		for (int i=1; i<=n; ++i) fa[i]=i, inc[i].emplace_back(i), siz[i]=1;
		for (int i=1; i<=n; ++i) a2[i]=a[i]=read(), b2[i]=b[i]=read();
		sta[++stop]=1; vis[1]=1;
		for (int i=2; i<=n; ++i) q.push(make(-1.0*a[i]/b[i], i));
		pair<double, int> u;
		while (q.size()) {
			u=q.top(); q.pop();
			// cout<<"u: "<<u.fir<<' '<<u.sec<<endl;
			if (u.sec!=fa[u.sec]) continue;
			// u.sec=find(u.sec);
			if (vis[find(u.sec)]) continue;
			if (vis[find(top[u.sec])]) {vis[u.sec]=1; for (auto it:inc[u.sec]) sta[++stop]=it; continue;}
			// cout<<"top: "<<top[u.sec]<<endl;
			uni(find(top[u.sec]), u.sec);
			u.sec=find(u.sec);
			q.push(make(-1.0*a[u.sec]/b[u.sec], u.sec));
		}
		ll ans=0;
		for (int i=n; i; --i) suf[i]=suf[i+1]+a2[sta[i]];
		for (int i=1; i<=n; ++i) ans+=b2[sta[i]]*suf[i+1];
		// cout<<"sta: "; for (int i=1; i<=stop; ++i) cout<<sta[i]<<' '; cout<<endl;
		printf("%lld\n", ans);
		exit(0);
	}
}

signed main()
{
	freopen("data.in", "r", stdin);
	freopen("data.out", "w", stdout);

	n=read();
	// if (n<=20) task2::solve();
	// else task1::solve();
	task::solve();
	
	return 0;
}