結果

問題 No.1976 Cut then Connect
ユーザー Demystify
提出日時 2022-06-10 23:17:54
言語 C++17
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 86 ms / 2,000 ms
コード長 9,258 bytes
コンパイル時間 2,496 ms
コンパイル使用メモリ 210,740 KB
最終ジャッジ日時 2025-01-29 20:18:31
ジャッジサーバーID
（参考情報） 		judge3 / judge1
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ファイルパターン 結果
sample AC * 2
other AC * 31
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ソースコード

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プレゼンテーションモードにする

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
// --------------------------------------------------------
#define FOR(i,l,r) for (ll i = (l); i < (r); ++i)
#define RFOR(i,l,r) for (ll i = (r)-1; (l) <= i; --i)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) RFOR(i,0,n)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define SORT(c) sort(ALL(c))
#define RSORT(c) sort(RALL(c))
#define MIN(c) *min_element(ALL(c))
#define MAX(c) *max_element(ALL(c))
#define COUNT(c,v) count(ALL(c),(v))
#define SZ(c) ((ll)(c).size())
#define BIT(b,i) (((b)>>(i)) & 1)
#define PCNT(b) __builtin_popcountll(b)
#define P0(i) (((i) & 1) == 0)
#define P1(i) (((i) & 1) == 1)
#define LB(c,v) distance((c).begin(), lower_bound(ALL(c), (v)))
#define UB(c,v) distance((c).begin(), upper_bound(ALL(c), (v)))
#define UQ(c) SORT(c), (c).erase(unique(ALL(c)), (c).end())
#define elif else if
#ifdef _LOCAL
    #define debug_bar cerr << "--------------------\n";
    #define debug(x) cerr << "l." << __LINE__ << " : " << #x << " = " << (x) << '\n'
    #define debug_pair(x) cerr << "l." << __LINE__ << " : " << #x << " = (" << x.first << "," << x.second << ")\n";
    template<class T> void debug_line(const vector<T>& ans, int l, int r, int L = 0) { cerr << "l." << L << " :"; for (int i = l; i < r; i++) { cerr 
        << ' ' << ans[i]; } cerr << '\n'; }
#else
    #define cerr if (false) cerr
    #define debug_bar
    #define debug(x)
    #define debug_pair(x)
    template<class T> void debug_line([[maybe_unused]] const vector<T>& ans, [[maybe_unused]] int l, [[maybe_unused]] int r, [[maybe_unused]] int L = 
        0) {}
#endif
template<class... T> void input(T&... a) { (cin >> ... >> a); }
void print() { cout << '\n'; }
template<class T> void print(const T& a) { cout << a << '\n'; }
template<class T, class... Ts> void print(const T& a, const Ts&... b) { cout << a; (cout << ... << (cout << ' ', b)); cout << '\n'; }
template<class T> void cout_line(const vector<T>& ans, int l, int r) { for (int i = l; i < r; i++) { if (i != l) { cout << ' '; } cout << ans[i]; } 
    cout << '\n'; }
template<class T> bool chmin(T& a, const T b) { if (b < a) { a = b; return 1; } return 0; }
template<class T> bool chmax(T& a, const T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> T SUM(const vector<T>& A) { return accumulate(ALL(A), T(0)); }
template<class T> vector<T> cumsum(const vector<T>& A, bool offset = true) { int N = A.size(); vector<T> S(N+1, 0); for (int i = 0; i < N; i++) { S[i
    +1] = S[i] + A[i]; } if (not offset) { S.erase(S.begin()); } return S; }
ll mod(ll x, ll m) { assert(m != 0); return (x % m + m) % m; }
ll ceil(ll a, ll b) { if (b < 0) { return ceil(-a, -b); } assert(b > 0); return (a < 0 ? a / b : (a + b - 1) / b); }
ll floor(ll a, ll b) { if (b < 0) { return floor(-a, -b); } assert(b > 0); return (a > 0 ? a / b : (a - b + 1) / b); }
ll powint(ll x, ll n) { assert(n >= 0); if (n == 0) { return 1; }; ll res = powint(x, n>>1); res *= res; if (n & 1) { res *= x; } return res; }
pair<ll,ll> divmod(ll a, ll b) { assert(b != 0); ll q = floor(a, b); return make_pair(q, a - q * b); }
ll bitlen(ll b) { if (b <= 0) { return 0; } return (64LL - __builtin_clzll(b)); }
ll digit_len(ll n) { assert(n >= 0); if (n == 0) { return 1; } ll sum = 0; while (n > 0) { sum++; n /= 10; } return sum; }
ll digit_sum(ll n) { assert(n >= 0); ll sum = 0; while (n > 0) { sum += n % 10; n /= 10; } return sum; }
ll digit_prod(ll n) { assert(n >= 0); if (n == 0) { return 0; } ll prod = 1; while (n > 0) { prod *= n % 10; n /= 10; } return prod; }
ll xor_sum(ll x) { assert(0 <= x); switch (x % 4) { case 0: return x; case 1: return 1; case 2: return x ^ 1; case 3: return 0; } assert(false); }
string toupper(const string& S) { string T(S); for (int i = 0; i < (int)T.size(); i++) { T[i] = toupper(T[i]); } return T; }
string tolower(const string& S) { string T(S); for (int i = 0; i < (int)T.size(); i++) { T[i] = tolower(T[i]); } return T; }
int a2i(const char& c) { assert(islower(c)); return (c - 'a'); }
int A2i(const char& c) { assert(isupper(c)); return (c - 'A'); }
int d2i(const char& d) { assert(isdigit(d)); return (d - '0'); }
char i2a(const int& i) { assert(0 <= i && i < 26); return ('a' + i); }
char i2A(const int& i) { assert(0 <= i && i < 26); return ('A' + i); }
char i2d(const int& i) { assert(0 <= i && i <= 9); return ('0' + i); }
using P = pair<ll,ll>;
using VP = vector<P>;
using VVP = vector<VP>;
using VS = vector<string>;
using VVS = vector<VS>;
using VI = vector<int>;
using VVI = vector<VI>;
using VVVI = vector<VVI>;
using VLL = vector<ll>;
using VVLL = vector<VLL>;
using VVVLL = vector<VVLL>;
using VB = vector<bool>;
using VVB = vector<VB>;
using VVVB = vector<VVB>;
using VD = vector<double>;
using VVD = vector<VD>;
using VVVD = vector<VVD>;
using VLD = vector<ld>;
using VVLD = vector<VLD>;
using VVVLD = vector<VVLD>;
const ld EPS = 1e-10;
const ld PI  = acosl(-1.0);
constexpr ll MOD = 1000000007;
// constexpr ll MOD = 998244353;
constexpr int inf = (1 << 30) - 1;   // 1073741824 - 1
constexpr ll INF = (1LL << 62) - 1;  // 4611686018427387904 - 1
// --------------------------------------------------------
// #include <atcoder/all>
// using namespace atcoder;
// References:
//   <https://null-mn.hatenablog.com/entry/2020/04/14/124151>
//   <https://qiita.com/keymoon/items/2a52f1b0fb7ef67fb89e>
//   <https://hcpc-hokudai.github.io/archive/dynamic_programming_rerooting.pdf>
//   <https://algo-logic.info/tree-dp/>
//   <https://github.com/atcoder/ac-library/blob/master/atcoder/segtree.hpp> (for implementation)
/**
 * @brief 全方位木 DP (Rerooting DP)
 * 
 * @tparam S モノイドの型 (結合律を満たし単位元が存在する代数構造)
 * @tparam (*op)(S,S) 二項演算
 * @tparam (*fv)(S,int,bool) 頂点に対する関数 (第2引数は頂点番号,第3引数は根であるか)
 * @tparam (*fe)(S,int,int,ll) 有向辺に対する関数 (第2/3引数は始点/終点番号,第4引数は重み)
 * @tparam (*e)() 単位元
 */
template <class S, S (*op)(S, S), S (*fv)(S, int, bool), S (*fe)(S, int, int, ll), S (*e)()>
struct rerooting {
    int N;
    vector<vector<pair<int,ll>>> G;
    vector<vector<S>> dp;  // dp[u][i] := u から出る i 番目の有向辺の先の部分木に対応する値
    // vector<S> ans;  // ans[u] := u を根とした木に対する答え
    ll ans = INF;
    rerooting(int n) : N(n) {
        // G.resize(N); dp.resize(N); ans.resize(N);
        G.resize(N); dp.resize(N);
    }
    // 頂点 u から頂点 v に有向辺を張る
    //   - 無向グラフの場合は両方向を追加する必要あり
    void add_edge(int u, int v, ll w) {
        assert(0 <= u && u < N);
        assert(0 <= v && v < N);
        G[u].emplace_back(v, w);
    }
    void build() {
        for (int u = 0; u < N; u++) { dp[u].resize(G[u].size()); }
        dfs1(0, -1);
        dfs2(0, -1, e());
    }
    S dfs1(int u, int p) {
        S res = e();
        int m = G[u].size();
        for (int i = 0; i < m; i++) {
            auto [v, w] = G[u][i];
            if (v == p) continue;
            dp[u][i] = dfs1(v, u);
            res = op(res, fe(dp[u][i], u, v, w));
        }
        return fv(res, u, true);
    }
    void dfs2(int u, int p, S px) {
        int m = G[u].size();
        for (int i = 0; i < m; i++) {
            auto [v, _] = G[u][i];
            if (v == p) { dp[u][i] = px; break; }
        }
        vector<S> dp_R(m+1);
        dp_R[m] = e();
        for (int i = m; 0 < i; i--) {
            auto [v, w] = G[u][i-1];
            dp_R[i-1] = op(fe(dp[u][i-1], u, v, w), dp_R[i]);
        }
        // ans[u] = fv(dp_R[0], u, false);
        S dp_l = e();
        for (int i = 0; i < m; i++) {
            auto [v, w] = G[u][i];
            if (v != p) dfs2(v, u, fv(op(dp_l, dp_R[i+1]), u, true));
            S s1 = op(dp_l, dp_R[i+1]);
            S s2 = dp[u][i];
            ll res = 0;
            chmax(res, ceil(s1.d, 2) + ceil(s2.d, 2) + 1);
            chmax(res, max(s1.d, s2.d));
            chmin(ans, res);
            // if (ceil(s1.d, 2) + ceil(s2.d, 2) + 1 == 3) {
            //     debug_pair(make_pair(u+1, v+1));
            //     debug_pair(make_pair(s1.d, s2.d));
            // }
            dp_l = op(dp_l, fe(dp[u][i], u, v, w));
        }
    }
    // S query(int u) const noexcept {
    //     assert(0 <= u && u < N);
    //     return ans[u];
    // }
};
struct S{
    ll d = 0;
    ll depth = 0;
};
S op(S a, S b) {
    a.d = max({a.d, b.d, a.depth + b.depth});
    a.depth = max(a.depth, b.depth);
    return a;
};
S fv(S x, [[maybe_unused]] int u, [[maybe_unused]] bool is_root) {
    return x;
};
S fe(S x, [[maybe_unused]] int s, [[maybe_unused]] int t, [[maybe_unused]] ll w) {
    x.depth++;
    return x;
};
S e() { return {0, 0}; };
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);
    ll N; cin >> N;
    rerooting<S, op, fv, fe, e> re(N);
    // const auto& G = re.G;
    REP(_,N-1) {
        ll u, v; cin >> u >> v;
        u--; v--;
        re.add_edge(u, v, 0);
        re.add_edge(v, u, 0);
    }
    re.build();
    ll ans = re.ans;
    print(ans);
    return 0;
}
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