题解 | #升！龙！！#

记录每个节点的树上前缀和(pref)以及以该节点为根节点到叶子节点的最大权值和(dp)，x被放到y的结点下面，那么以x为根节点的子树就废了，把pref[y]加上dp[x]，并且忽略这棵子树，可以通过前序遍历的编号来确定子树的范围，通过线段树来维护前缀值

#include <bits/stdc++.h>
using namespace std;
using ll=long long;
#define len(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define db(x) cerr << #x << "=" << (x) << " "
#define el cerr << "\n"

const int MN=2e5;
vector<int> adj[MN+5];
ll pref[MN+5], dp[MN+5], a[MN+5];
int siz[MN+5], dfn[MN+5], id;

template<class Info>
class SegmentTree {
private:
    int n;
    vector<Info> info, a;
public:
    SegmentTree(int n) {
        this->n=n;
        info.resize(4*n+1);
        this->a=a;
        build(1, 1, n);
    }
    void build(int id, int l, int r) {
        if (l==r) {
            info[id]=Info();
            return;
        }
        int mid=(l+r)/2;
        build(id*2, l, mid);
        build(id*2+1, mid+1, r);
        info[id]=info[id*2]+info[id*2+1];
    }
    void modify(int id, int l, int r, int p, const Info& v) {
        if (l==r) {
            info[id]=v;
            return;
        }
        int mid=(l+r)/2;
        if (p<=mid)
            modify(id*2, l, mid, p, v);
        else
            modify(id*2+1, mid+1, r, p, v);
        info[id]=info[id*2]+info[id*2+1];
    }
    void modify(int p, const Info& v) {
        p++;
        modify(1, 1, n, p, v);
    }
    Info query(int id, int l, int r, int s, int e) {
        if (s<=l && e>=r) {
            return info[id];
        }
        if (r<s || l>e) {
            return Info();
        }
        int mid=(l+r)/2;
        return query(id*2, l, mid, s, e)+query(id*2+1, mid+1, r, s, e);
    }
    Info query(int l, int r) {
        l++, r++;
        return query(1, 1, n, l, r);
    }
};

class Info {
public:
    ll x;

    Info() {
        this->x=0;
    }
    Info(ll x) {
        this->x=x;
    }
};

Info operator+(const Info& a, const Info& b) {
    Info c;
    c.x=max(a.x, b.x);
    return c;
}

void dfs(int u, int p) {
    dfn[u]=++id;
    dp[u]=a[u];
    siz[u]=1;
    pref[u]=pref[p]+a[u];
    ll mx=0;
    for (int v : adj[u]) {
        if (v==p)
            continue;
        dfs(v, u);
        siz[u]+=siz[v];
        mx=max(mx, dp[v]);
    }
    dp[u]+=mx;
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int n, q;
    cin >> n >> q;
    vector<int> p(n+1);
    for (int i=1; i<=n; i++) {
        cin >> a[i];
    }
    for (int i=2; i<=n; i++) {
        cin >> p[i];
        adj[p[i]].push_back(i);
        adj[i].push_back(p[i]);
    }
    dfs(1, 0);
    SegmentTree<Info> seg(n+1);
    for (int i=1; i<=n; i++) {
        seg.modify(dfn[i], pref[i]);
    }
    while (q--) {
        int x, y;
        cin >> x >> y;
        Info oldv=seg.query(dfn[y], dfn[y]);
        Info newv=oldv;
        newv.x+=dp[x];
        seg.modify(dfn[y], newv);
        int l=dfn[x];
        int r=l+siz[x]-1;
        ll ans=seg.query(1, l-1).x;
        ans=max(ans, seg.query(r+1, n).x);
        cout << ans << "\n";
        seg.modify(dfn[y], oldv);
    }
    return 0;
}