https://ac.nowcoder.com/acm/contest/49244/D
[排序不等式][单链表]

#include<bits/stdc++.h>
#define endl '\n'
using namespace std;
const int N = 3e5 + 10;
int e[N], ne[N], idx, h[N];
int num[N],a[N];
void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}
void dfs(int u)
{
    num[u] = 1;
    for (int i = h[u]; i != -1; i=ne[i])
    {
        int j = e[i];
        dfs(j);
        num[u] += num[j];
    }
}
int main()
{
    int n;
    cin >> n;
    memset(h, -1, sizeof h);
    for (int i = 1; i <= n; i++)
        cin >> a[i];
    for (int i = 2; i <= n; i++)
    {
        int x;
        cin >> x;
        add(x, i);
    }
    dfs(1);
    sort(a + 1, a + n + 1);
    sort(num + 1, num + n + 1);
    long long sum = 0;
    for (int i = 1; i <= n; i++)
    {
        sum += (long long)a[i] * num[i];
    }
    cout << sum << endl;
    return 0;
}