192 lines
3.7 KiB
C++
192 lines
3.7 KiB
C++
/* Problem URL: https://codeforces.com/problemset/problem/1975/D */
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#include <bits/stdc++.h>
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#include <ext/pb_ds/assoc_container.hpp>
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#include <ext/pb_ds/tree_policy.hpp>
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using namespace std;
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using namespace __gnu_pbds;
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template <class T, class comp = less<>>
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using ordered_set = tree<T, null_type , comp , rb_tree_tag , tree_order_statistics_node_update>;
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#define V vector
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#define rmin(a, b) a = min(a, b)
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#define rmax(a, b) a = max(a, b)
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#define rep(i, lim) for (int i = 0; i < (lim); i++)
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#define nrep(i, s, lim) for (int i = s; i < (lim); i++)
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#define repv(i, v) for (auto &i : (v))
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#define fillv(v) for (auto &itr_ : (v)) { cin >> itr_; }
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#define sortv(v) sort(v.begin(), v.end())
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#define all(v) (v).begin(), (v).end()
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using vi = vector<int>;
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using vvi = vector<vi>;
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using vvvi = vector<vvi>;
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using vvvvi = vector<vvvi>;
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using ll = long long;
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using vl = vector<ll>;
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using vvl = vector<vl>;
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using vvvl = vector<vvl>;
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using vvvvl = vector<vvvl>;
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template<class v>
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auto operator<<(ostream &os, const vector<v> &vec)->ostream& {
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os << vec[0];
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for (size_t i = 1; i < vec.size(); i++) {
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os << ' ' << vec[i];
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}
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os << '\n';
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return os;
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}
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template<class v>
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auto operator>>(istream &is, vector<v> &vec)->istream& {
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for (auto &i : vec) {
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is >> i;
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}
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return is;
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}
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template<class v>
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auto operator<<(ostream &os, const vector<vector<v>> &vec)->ostream& {
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for (auto &i : vec) {
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os << i[0];
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for (size_t j = 1; j < i.size(); j++) {
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os << ' ' << i[j];
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}
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os << '\n';
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}
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return os;
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}
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template<class v>
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auto operator>>(istream &is, vector<vector<v>> &vec)->istream& {
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for (auto &i : vec) {
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for (auto &j : i) {
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is >> j;
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}
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}
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return is;
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}
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const int oo = INT32_MAX >> 1;
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const ll OO = INT64_MAX >> 1;
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void pre()
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{
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}
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#define TEST 1
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void solve()
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{
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int n, a, b;
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cin >> n >> a >> b;
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a--, b--;
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vvi graph(n);
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rep(i, n - 1) {
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int u, v;
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cin >> u >> v;
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u--, v--;
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graph[u].push_back(v);
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graph[v].push_back(u);
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}
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auto bfs = [&](vi &dis, int a) {
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queue<int> q;
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dis[a] = 0;
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q.push(a);
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while (!q.empty()) {
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int i = q.front();
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q.pop();
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repv(j, graph[i]) {
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if (dis[j] > dis[i] + 1) {
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dis[j] = dis[i] + 1;
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q.push(j);
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}
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}
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}
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};
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vi disa(n, oo);
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vi disb(n, oo);
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bfs(disa, a);
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bfs(disb, b);
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vi dp(n);
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function<int(int, int)> calc = [&](int i, int p) {
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repv(j, graph[i]) {
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if (j == p) {
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continue;
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}
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rmax(dp[i], calc(j, i) + 1);
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}
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return dp[i];
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};
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calc(0, 0);
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ll ans = OO;
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function<void(int, int)> reroot = [&](int i, int p) {
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int first = 0;
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int second = 0;
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repv(j, graph[i]) {
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if (dp[j] >= first) {
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second = first;
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first = dp[j] + 1;
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continue;
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}
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rmax(second, dp[j] + 1);
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}
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rmin(ans, max(disb[i], disa[i]) + (disa[i] > disb[i] && (disb[i] & 1) != (disa[i] & 1)) + (ll)(n - 1) * 2 - first);
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repv(j, graph[i]) {
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if (j == p) {
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continue;
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}
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if (dp[j] == first - 1) {
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dp[i] = second;
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} else {
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dp[i] = first;
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}
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reroot(j, i);
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}
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};
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reroot(0, 0);
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cout << ans << '\n';
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}
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int main()
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{
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ios::sync_with_stdio(false);
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cin.tie(nullptr);
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pre();
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int t;
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(TEST && cin >> t) || (t = 1);
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while (t--) {
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solve();
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}
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}
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