Mo's on tree (Query on subtree)

#include <bits/stdc++.h>
#define ll long long
#define SaveTime ios_base::sync_with_stdio(false), cin.tie(0);
using namespace std;

struct query {
    int L,R,id;
    query() {
        L = R = id = 0;
    }
    query(int _L, int _R, int _id) {
        L = _L;
        R = _R;
        id = _id;
    }
};

int block;

bool cmp(query q1, query q2) {
    if (q1.L/block < q2.L/block)
        return true;
    if (q1.L/block == q2.L/block && q1.R < q2.R)
        return true;
    return false;
}

const int N = 2e5+7;
vector<vector<int>> tree(N);
int tin[N];
int tout[N];
bool visited[N];
vector<int> tim;

void dfs(int node, int par = -1) {
    tim.push_back(node);
    tin[node] = tim.size()-1;
    for (int ch : tree[node]) {
        if (ch != par) {
            dfs(ch, node);
        }
    }
    tim.push_back(node);
    tout[node] = tim.size()-1;
}

void ins(int id) {
    // if the node is visited just return 
}

void del(int id) {

}

int main() {
    int n,q; cin >> n >> q;
    block = 2*n/sqrt(q)+1;

    for (int i = 0; i < n-1; i++) {
        int a,b; cin >> a >> b;
        tree[a].push_back(b);
        tree[b].push_back(a);
    }
    dfs(1);
    query qr[q];
    for (int i = 0; i < q; i++) {
        int node; cin >> node;
        qr[i] = query(tin[node], tout[node], i);
    }
    sort(qr, qr+q, cmp);
    int ans[q];
    int l = 0, r = -1;
    for (int i = 0; i < q; i++) {
        auto [L,R,id] = qr[i];
        while (r < R) {
            r++;
            ins(r);
        }
        while (r > R) {
            del(r);
            r--;
        }
        while (l < L) {
            del(l);
            l++;
        }
        while (l > L) {
            l--;
            ins(l);
        }
    }
    for (int i = 0; i < q; i++) {
        cout << ans[i] << '\n';
    }
}

Problems :
https://codeforces.com/problemset/problem/375/D