제출 #284056

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
284056		Haunted_Cpp	Islands (IOI08_islands)	C++17	40 / 100	1452 ms	1968 KiB

islands

/**
 *  author: Haunted_Cpp
**/

#include <bits/stdc++.h>
using namespace std;

#pragma GCC optimize("Ofast")
#pragma GCC target("fma,sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#pragma GCC optimize("unroll-loops")

template<typename T> ostream &operator << (ostream &os, const vector<T> &v) { os << '{'; string sep; for (const auto &x : v) os << sep << x, sep = ", "; return os << '}'; }
template<typename T, size_t size> ostream &operator << (ostream &os, const array<T, size> &arr) { os << '{'; string sep; for (const auto &x : arr) os << sep << x, sep = ", "; return os << '}'; }
template<typename A, typename B> ostream &operator << (ostream &os, const pair<A, B> &p) { return os << '(' << p.first << ", " << p.second << ')'; }

void debug_out() { cerr << endl; }
template<typename Head, typename... Tail> void debug_out(Head H, Tail... T) { cerr << ' ' << H; debug_out(T...); }

#ifdef LOCAL
#define debug(...) cerr << "(" << #__VA_ARGS__ << "):", debug_out(__VA_ARGS__)
#else
#define debug(...) 47
#endif

const int MAX_N = 4e3 + 5;

int Time = 0;

vector<vector<pair<int, int>>> g(MAX_N);
vector<int> low(MAX_N), disc(MAX_N);

map<int, int> cnt[MAX_N];

set<pair<int, int>> all_edge;
set<pair<int, int>> bridge;

void is_valid_bridge(int st, int et) {
  if (max(cnt[st][et], cnt[et][st]) <= 1) {
    bridge.insert({st, et});
  }
}

void find_bridge(int node, int p) {
  low[node] = disc[node] = ++Time;
  for (auto to : g[node]) {
    const int et = to.first;
    all_edge.insert({node, et});
    if (et == p) continue;
    if (!disc[et]) {
      find_bridge(et, node);
      low[node] = min(low[node], low[et]);
      if (disc[node] < low[et]) {
       // cout << node << ' ' << et << '\n';
        is_valid_bridge(node, et);
      }
    } else {
      low[node] = min(low[node], disc[et]);
    }
  }
}

int blocked_st, blocked_et;
pair<long long, int> dist;

void dfs(int node, int p, long long w) {
  dist = max(dist, {w, node});
  for (auto to : g[node]) {
    const int et = to.first;
    const int cost = to.second;
    if (et == p) continue;
    if (cnt[node][et] == 1) {
      if (blocked_st == node && blocked_et == et) continue;
      if (blocked_et == node && blocked_st == et) continue;
    }
    dfs(et, node, w + cost);
  }
}

long long find_diameter(int node) {
  dist = {-1, -1};
  dfs(node, -1, 0);
  node = dist.second;
  dfs(node, -1, 0);
  return dist.first;
}

int main () {
  ios::sync_with_stdio(0);
  cin.tie(nullptr);
  int n;
  cin >> n;
  for (int st = 0; st < n; st++) {
    int et, w;
    cin >> et >> w;
    --et;
    ++cnt[st][et];
    ++cnt[et][st];
    g[st].emplace_back(et, w);
    g[et].emplace_back(st, w);
  }
  long long best_way = 0;
  for (int i = 0; i < n; i++) {
    if (!disc[i]) {
      all_edge = set<pair<int, int>>();
      bridge = set<pair<int, int>>();
      find_bridge(i, -1);
      long long res = 0;
      for (auto to : all_edge) {
        if (bridge.find({to.first, to.second}) != bridge.end() || bridge.find({to.second, to.first}) != bridge.end()) continue;
        blocked_st = to.first;
        blocked_et = to.second;
        res = max(res, find_diameter(i));
      }
      best_way += res;
    }
  }
  cout << best_way << '\n';
  return 0;
}

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