MMSet2

题目地址：

https://ac.nowcoder.com/acm/problem/14250

基本思路：

参考代码:

#pragma GCC optimize(2)
#pragma GCC optimize(3)
#include <bits/stdc++.h>
using namespace std;
#define IO std::ios::sync_with_stdio(false); cin.tie(0)
#define ll long long
#define rint register int
#define SZ(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define rep(i, l, r) for (int i = l; i <= r; i++)
#define per(i, l, r) for (int i = l; i >= r; i--)
#define mset(s, _) memset(s, _, sizeof(s))
#define pb push_back
#define pii pair <int, int>
#define mp(a, b) make_pair(a, b)
#define INF 0x3f3f3f3f

inline int read() {
  int x = 0, neg = 1; char op = getchar();
  while (!isdigit(op)) { if (op == '-') neg = -1; op = getchar(); }
  while (isdigit(op)) { x = 10 * x + op - '0'; op = getchar(); }
  return neg * x;
}
inline void print(ll x) {
  if (x < 0) { putchar('-'); x = -x; }
  if (x >= 10) print(x / 10);
  putchar(x % 10 + '0');
}

const int maxn = (int)3e5 + 10;
int n, q;
struct Edge {
    int to, next, val;
} edge[maxn << 1];
int head[maxn], cnt;
void add_edge(int u, int v, int w) {
  edge[++cnt] = {v, head[u], w};
  head[u] = cnt;
}
ll dis[maxn];
int lg[maxn << 1], a[maxn << 1], dfn[maxn], dep[maxn], tot;
int f[maxn << 1][20];
void dfs(int u, int fa) {
  f[++tot][0] = u, dfn[u] = tot, dep[u] = dep[fa] + 1;
  for (rint i = head[u]; i; i = edge[i].next) {
    int v = edge[i].to;
    if (v == fa) continue;
    dis[v] = dis[u] + edge[i].val;
    dfs(v, u);
    f[++tot][0] = u;
  }
}
void pre() {
  lg[1] = 0;
  for (rint i = 2; i <= tot; i++) lg[i] = lg[i >> 1] + 1;
  for (rint j = 1; j <= 19; j++) {
    for (rint i = 1; i + (1 << j) - 1 <= tot; i++) {
      if (dep[f[i][j - 1]] < dep[f[i + (1 << j - 1)][j - 1]]) {
        f[i][j] = f[i][j - 1];
      } else {
        f[i][j] = f[i + (1 << j - 1)][j - 1];
      }
    }
  }
}
int LCA(int u, int v) {
  u = dfn[u], v = dfn[v];
  if (u > v) swap(u, v);
  int len = lg[v - u + 1];
  if (dep[f[u][len]] < dep[f[v - (1 << len) + 1][len]]) {
    return f[u][len];
  } else {
    return f[v - (1 << len) + 1][len];
  }
}
ll dist(int u, int v) { return dis[u] + dis[v] - 2ll * dis[LCA(u, v)]; }

signed main() {
  IO;
  n = read();
  rep(i,1,n - 1) {
    int u = read(), v = read();
    add_edge(u, v, 1);
    add_edge(v, u, 1);
  }
  dfs(1,0); pre();
  q = read();
  while (q--){
    int k = read();
    vector<int> memo;
    int m = 0;
    rep(i,1,k){
      int x = read();
      if(dep[x] > dep[m]) m = x;
      memo.push_back(x);
    }
    ll mx = 0;
    for(auto it : memo){
      mx = max(mx,dist(it,m));
    }
    ll res = (mx + 1) / 2;
    print(res);
    puts("");
  }
  return 0;
}