点权和

思路：建树->对树进行更新维护->输出

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cctype>
#include <algorithm>
using namespace std;
#define rep(i, s, t) for(int i = (s); i <= (t); i++)
#define dwn(i, s, t) for(int i = (s); i >= (t); i--)

int read() {
    int x = 0, f = 1; char c = getchar();
    while(!isdigit(c)){ if(c == '-') f = -1; c = getchar(); }
    while(isdigit(c)){ x = x * 10 + c - '0'; c = getchar(); }
    return x * f;
}

#define maxn 100010
#define MOD 19260817
#define LL long long

int n, q, fa[maxn], m, head[maxn], nxt[maxn], to[maxn];

void AddEdge(int a, int b) {
    to[++m] = b; nxt[m] = head[a]; head[a] = m;
    return ;
}

int bel[maxn], siz[maxn], add[maxn], sum[maxn], indi[maxn];
void build(int u) {
    for(int e = head[u]; e; e = nxt[e]) if(to[e] != fa[u])
        bel[to[e]] = u, siz[u]++, build(to[e]);
    return ;
}

int main() {
    n = read(); q = read();
    rep(i, 2, n) fa[i] = read(), AddEdge(fa[i], i);

    bel[1] = 0; siz[0] = 1;
    build(1);
    int Ans = 0;
    rep(i, 1, q) {
        int x = read();
        sum[x] += siz[x];
        if(sum[x] >= MOD) sum[x] -= MOD;
        add[x]++;
        indi[x]++; sum[bel[x]]++; if(sum[bel[x]] >= MOD) sum[bel[x]] -= MOD;
        if(fa[x]) {
            indi[fa[x]]++; sum[bel[fa[x]]]++;
            if(sum[bel[fa[x]]] >= MOD) sum[bel[fa[x]]] -= MOD;
        }
        int nowans = (sum[x] + indi[x] + add[bel[x]]) % MOD;
        if(fa[x]) (nowans += indi[fa[x]] + add[bel[fa[x]]]) %= MOD;
        Ans += (LL)nowans * i % MOD;
        if(Ans >= MOD) Ans -= MOD;
    }

    printf("%d\n", Ans);

    return 0;
}