Friends & Enemies, DSU type, CF

/**
 *    author:  compounding
 *    created: 2024-12-15 16:52:14
 **/
#include <bits/stdc++.h>
using namespace std;
mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());
#define NeedForSpeed                  \
    ios_base::sync_with_stdio(false); \
    cin.tie(NULL);                    \
    cout.tie(NULL);
#define int long long
#define all(x) (x).begin(), (x).end()
typedef vector<int> vi;
typedef vector<bool> vb;
typedef vector<vi> vvi;
typedef vector<pair<int, int>> vpi;
#define f first
#define s second
#define yes cout << "YES" << endl
#define no cout << "NO" << endl
#define endl "\n"
const int mod = 1000000007;
int gcd(int a, int b) { return b == 0 ? a : gcd(b, a % b); }
const int N = 2005;
vi friends[N];
vi enemies[N];
vi visf(N, 0);
vi visitednow(N, 0);
vi vise(N, 0);
bool check = true;
int counts, ans, n;

void dfs1(int node)
{
    visf[node] = 1;
    visitednow[node] = 1;
    counts++;
    for (auto child : friends[node])
    {
        if (!visf[child])
        {
            dfs1(child);
        }
    }
}

void dfs2(int node, int parent)
{
    vise[node] = 1;
    // if anynode is and its adj neighbour is visited means they are enemy but have been counted as friend
    if (visitednow[node])
    {
        for (auto &enemy : enemies[node])
        {
            if (visitednow[enemy])
            {
                check = false;
                return;
            }
        }
    }
    for (auto &child : friends[node])
    {
        if (child == parent || vise[child])
        {
            continue;
        }
        dfs2(child, node);
    }
}

void solve()
{
    cin >> n;
    int k; // number of pairs of friends
    cin >> k;
    for (int i = 0; i < k; i++)
    {
        int a, b;
        cin >> a >> b;
        friends[a].push_back(b);
        friends[b].push_back(a);
    }
    int m;
    cin >> m; // number of pairs of enemies
    for (int i = 0; i < m; i++)
    {
        int a, b;
        cin >> a >> b;
        enemies[a].push_back(b);
        enemies[b].push_back(a);
    }
    visf = vi(N, 0);
    ans = 0;
    for (int i = 1; i <= n; i++)
    {
        if (visf[i])
        {
            continue;
        }
        vise = vi(N, 0);
        visitednow = vi(N, 0);
        counts = 0, check = true;
        dfs1(i);
        for (int j = 1; j <= n; j++)
        {
            if (visitednow[j])
            {
                dfs2(j, -1);
            }
        }
        if (check)
        {
            ans = max(ans, counts);
        }
    }
    cout << ans << endl;
    return;
}

signed main()
{
    NeedForSpeed;
    int t = 1;
    // cin >> t;
    while (t--)
    {
        solve();
    }
    return 0;
}