Lemda_function_02

auto dfs = [&](ll u, ll parent, auto&& self) -> ll {
    ll mx1 = 0, mx2 = 0;

    for (auto v : adj[u]) {
        if (v != parent) {
            ll tmp = self(v, u, self); // Use self for recursion

            if (tmp > mx1) {
                mx2 = mx1;
                mx1 = tmp;
            } else if (tmp > mx2) {
                mx2 = tmp;
            }
        }
    }

    res = max(res, mx1 + mx2 + val[u]);
    return max(mx1, mx2) + val[u];
};