rt,wa on #5

#include <bits/stdc++.h>

using namespace std;

const int MAXN = 2e5 + 5;

struct Node {
  int v, fa;
  vector<int> s;
} a[MAXN];

struct Node1 {
  int cnt0, cnt1, fa;
} bcj[MAXN];

int fa(int x) {
  if (bcj[x].fa == x) return x;
  return bcj[x].fa = fa(bcj[x].fa);
}

void shit(int u, int v) {
  u = fa(u), v = fa(v);
  bcj[v].cnt0 += bcj[u].cnt0;
  bcj[v].cnt1 += bcj[u].cnt1;
  bcj[u].cnt0 = bcj[u].cnt1 = 0;
  bcj[u].fa = v;
}

void dfs(int x) {
  if (a[x].fa > -1) {
    if (a[x].v < a[a[x].fa].v) {
      shit(x, a[x].fa);
    } else {
      int u = fa(a[x].fa);
      while (a[u].fa > -1 && 1ll * bcj[u].cnt1 * bcj[fa(a[u].fa)].cnt0 < 1ll * bcj[u].cnt0 * bcj[fa(a[u].fa)].cnt1) {
        shit(u, fa(a[u].fa));
        u = fa(u);
      }
    }
  }
  for (int nx : a[x].s) {
    dfs(nx);
  }
}

struct Node2 {
  int x, cnt0, cnt1;
  bool operator>(const Node2& a) const {
    return 1ll * cnt0 * a.cnt1 > 1ll * a.cnt0 * cnt1;
  }
  bool operator<(const Node2& a) const {
    return 1ll * cnt0 * a.cnt1 < 1ll * a.cnt0 * cnt1;
  }
};

priority_queue<Node2> q;

int n, ans = 0, cnt = 0;

void dfs2(int x) {
  if (a[x].v > 0) {
    ans += cnt;
  } else {
    --cnt;
  }
  for (int nx : a[x].s) {
    if (fa(nx) == fa(x)) {
      dfs2(nx);
    } else {
      q.push({fa(nx), bcj[fa(nx)].cnt0, bcj[fa(nx)].cnt1});
    }
  }
}

int main() {
  ios_base :: sync_with_stdio(0), cin.tie(0), cout.tie(0);
  cin >> n;
  a[1].fa = -1;
  for (int i = 2; i <= n; ++i) {
    cin >> a[i].fa;
    a[a[i].fa].s.push_back(i);
  }
  for (int i = 1; i <= n; ++i) {
    cin >> a[i].v;
    bcj[i] = {0, 0, i};
    if (a[i].v > 0) {
      bcj[i].cnt1 = 1;
    } else {
      bcj[i].cnt0 = 1;
      ++cnt;
    }
  } 
  dfs(1);
  q.push({fa(1), bcj[fa(1)].cnt0, bcj[fa(1)].cnt1});
  while (!q.empty()) {
    Node2 nx = q.top();
    q.pop();
    dfs2(nx.x);
  }
  cout << ans;
  return 0;
}