Submission #601487

#	Time	Username	Problem	Language	Result	Execution time	Memory
601487		narvalo	Ferries (NOI13_ferries)	C++17	33 / 40	477 ms	33988 KiB

ferries

#include <bits/stdc++.h>

using namespace std;

#define int long long

const int INF = (int)1e18;

int ferries(int n , int m , vector<vector<pair<int , int>>> adj) {
  vector<int> dp(n , -1);
  function<long long(int)> Solve = [&](int node) -> long long {
    if (node == n - 1) {
      return 0;
    }
    if (dp[node] != -1) {
      return dp[node];
    }
    vector<int> d;
    for (auto x : adj[node]) {
      d.push_back(Solve(x.first));      
    }
    sort(d.begin() , d.end());
    vector<int> s;
    for (int i = 0 ; i < (int)adj[node].size() ; i += 1) {
      s.push_back(adj[node][i].second);
    }
    sort(s.begin() , s.end());
    auto Get = [&]() {
      int val = INF;
      for (int i = 0 ; i < (int)s.size() ; i += 1) {
        val = min(val , s[i] + d[(int)s.size() - i - 1]);
      }
      return val;
    };
    int res = Get();
    reverse(s.begin() , s.end());
    reverse(d.begin() , d.end());
    res = max(res , Get());
    return dp[node] = res;
  };
  int res = Solve(0);
  return res;
}

int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n , m;
  cin >> n >> m;
  vector<vector<pair<int , int>>> adj(n) , rev(n);
  vector<vector<int>> edges(n);
  for (int i = 0 ; i < m ; i += 1) {
    int a , b , c;
    cin >> a >> b >> c; 
    a -= 1 , b -= 1;
    edges[a].push_back(c);
    adj[a].emplace_back(b , c);
    rev[b].emplace_back(a , c);
  }
  bool ok = true;
  for (int i = 1 ; i < n - 1 ; i += 1) {
    ok &= ((int)adj[i].size() == 1);
  }
  if (ok) {
    int res = ferries(n , m , adj);
    cout << res << '\n';
    return 0;
  }
  for (int i = 0 ; i < n ; i += 1) {
    sort(edges[i].begin() , edges[i].end());
  }
  #define pi pair<int , int>
  priority_queue<pi , vector<pi> , greater<pi>> pq;
  vector<int> d(n , INF);
  d[n - 1] = 0;
  pq.emplace(d[n - 1] , n - 1);
  while (!pq.empty()) {
    auto t = pq.top();
    pq.pop();
    if (d[t.second] != t.first) continue;
    for (int i = 0 ; i < (int)rev[t.second].size() ; i += 1) {
      auto node = rev[t.second][i];
      vector<pair<int , int>> c2;
      for (auto x : adj[node.first]) {
        c2.emplace_back(d[x.first] , x.first);
      }
      sort(c2.begin() , c2.end());

      for (int j = 0 ; j < (int)edges[node.first].size() ; j++) {
        int new_id = (int)edges[node.first].size() - j - 1;
        int id = c2[new_id].second;
        if (id == t.second) {
          if (d[node.first] > t.first + edges[node.first][j]) {
            d[node.first] = t.first + edges[node.first][j];
            pq.emplace(d[node.first] , node.first);
          }
          break;
        }
        else continue;
      }
    }
  }
  cout << d[0] << '\n';
  return 0; 
}

• Subtask 1: 0 / 7
• Subtask 2: 10 / 10
• Subtask 3: 11 / 11
• Subtask 4: 12 / 12