結果

問題 No.1833 Subway Planning
コンテスト
ユーザー Sumitacchan
提出日時 2022-02-05 00:10:54
言語 C++17
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 845 ms / 4,000 ms
コード長 4,001 bytes
コンパイル時間 2,555 ms
コンパイル使用メモリ 208,676 KB
最終ジャッジ日時 2025-01-27 20:14:16
ジャッジサーバーID
（参考情報） 		judge3 / judge3
このコードへのチャレンジ
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ファイルパターン 結果
sample AC * 3
other AC * 23
権限があれば一括ダウンロードができます

ソースコード

diff # 

#include <bits/stdc++.h>
using namespace std;
//using namespace atcoder;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define FOR(i, begin, end) for(int i=(begin);i<(end);i++)
#define REP(i, n) FOR(i,0,n)
#define IFOR(i, begin, end) for(int i=(end)-1;i>=(begin);i--)
#define IREP(i, n) IFOR(i,0,n)
#define Sort(v) sort(v.begin(), v.end())
#define Reverse(v) reverse(v.begin(), v.end())
#define all(v) v.begin(),v.end()
#define SZ(v) ((int)v.size())
#define Lower_bound(v, x) distance(v.begin(), lower_bound(v.begin(), v.end(), x))
#define Upper_bound(v, x) distance(v.begin(), upper_bound(v.begin(), v.end(), x))
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
#define bit(n) (1LL<<(n))
#define debug(x) cout << #x << "=" << x << endl;
#define vdebug(v) { cout << #v << "=" << endl; REP(i_debug, (int)v.size()){ cout << v[i_debug] << ","; } cout << endl; }
#define mdebug(m) { cout << #m << "=" << endl; REP(i_debug, (int)m.size()){ REP(j_debug, (int)m[i_debug].size()){ cout << m[i_debug][j_debug] << ","; } cout << endl;} }
#define pb push_back
#define fi first
#define se second
#define int long long
#define INF 1000000000000000000
template<typename T> istream &operator>>(istream &is, vector<T> &v){ for (auto &x : v) is >> x; return is; }
template<typename T> ostream &operator<<(ostream &os, vector<T> &v){ for(int i = 0; i < (int)v.size(); i++) { cout << v[i]; if(i != (int)v.size() - 1) cout << endl; }; return os; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, pair<T1, T2> p){ cout << '(' << p.first << ',' << p.second << ')'; return os; }
template<typename T> void Out(T x) { cout << x << endl; }
template<typename T1, typename T2> void chOut(bool f, T1 y, T2 n) { if(f) Out(y); else Out(n); }

using vec = vector<int>;
using mat = vector<vec>;
using Pii = pair<int, int>;
using v_bool = vector<bool>;
using v_Pii = vector<Pii>;

//int dx[4] = {1,0,-1,0};
//int dy[4] = {0,1,0,-1};
//char d[4] = {'D','R','U','L'};

//const int mod = 1000000007;
const int mod = 998244353;

template<typename T> 
struct edge{ int to; T cost; int id; };

template<typename T = long long>
struct Graph
{

    int N;
    vector<vector<edge<T>>> E;
    vec depth, dp;

    Graph(int N): N(N){
        E = vector<vector<edge<T>>>(N, vector<edge<T>>(0));
        depth.resize(N);
        dp.resize(N);
    }

    void add_Directed_edge(int from, int to, T cost = 1, int id = 0){
        E[from].push_back(edge<T>({ to, cost, id }));
    }

    void add_Undirected_edge(int v1, int v2, T cost = 1, int id = 0){
        add_Directed_edge(v1, v2, cost, id);
        add_Directed_edge(v2, v1, cost, id);
    }

    void dfs1(int v, int d = 0, int p = -1){
        depth[v] = d;
        for(auto e: E[v]) if(e.to != p){
            dfs1(e.to, d + 1, v);
        }
    }

    bool dfs2(int v, const v_bool &used, int &mm, int p = -1){
        bool f = false;
        for(auto e: E[v]) if(e.to != p){
            bool f0 = used[e.id] | dfs2(e.to, used, mm, v);
            if(f && f0) mm = -INF;
            else if(f0) chmin(mm, e.cost);
            f = f || f0;
        }
        return f;
    }

};

signed main(){

    int N; cin >> N;
    Graph G(N);
    vec a(N - 1), b(N - 1), c(N - 1);
    int cmax = 0;
    REP(i, N - 1){
        cin >> a[i] >> b[i] >> c[i];
        a[i]--; b[i]--;
        G.add_Undirected_edge(a[i], b[i], c[i], i);
        chmax(cmax, c[i]);
    }
    G.dfs1(0);

    int ok = cmax, ng = -1;
    while(ok - ng > 1){
        int x = (ng + ok) / 2;
        v_bool used(N - 1, false);
        int d0 = -1, v0 = -1;
        REP(i, N - 1) if(c[i] > x){
            used[i] = true;
            for(int s: {a[i], b[i]}) if(G.depth[s] > d0){
                d0 = G.depth[s];
                v0 = s;
            }
        }
        int mm = INF;
        G.dfs2(v0, used, mm);
        if(cmax - mm <= x) ok = x;
        else ng = x;
    }
    cout << ok << endl;

    return 0;
}
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