Submission #601327

#	Time	Username	Problem	Language	Result	Execution time	Memory
601327		narvalo	Ferries (NOI13_ferries)	C++17	17 / 40	106 ms	22884 KiB

ferries

#include <bits/stdc++.h>

using namespace std;

int ferries(int n , int m , vector<int> a , vector<int> b , vector<int> c) {
  vector<vector<pair<int , int>>> adj(n);
  for (int i = 0 ; i < m ; i++) {
    a[i] -= 1 , b[i] -= 1;
    adj[a[i]].emplace_back(b[i] , c[i]);
  }
  vector<int> s , d;
  bool sub1 = ((int)s.size() == (int)d.size() && (int)s.size() == n - 2);
  bool sub2 = true;
  for (int i = 1 ; i < n - 1 ; i += 1) {
    sub2 |= ((int)adj[i].size() == 1);
  }
  vector<int> mx(n);
  for (int i = 0 ; i < n ; i++) {
    for (auto x : adj[i]) {
      mx[i] = max(mx[i] , x.second);
    }
  }
  
  if (sub1 || sub2) {
    if (sub1) {
      for (int i = 0 ; i < (int)adj[0].size() ; i += 1) {
        s.push_back(adj[0][i].second);
      }
      sort(s.begin() , s.end());
      for (int i = 1 ; i < n - 1 ; i += 1) {
        d.push_back(adj[i][0].second);
      }
      sort(d.begin() , d.end());
    }
    else {
      vector<int> vis(n);
      vis[0] = 1;
      vector<int> dp(n , -1);
      function<int(int)> Dfs = [&](int node) {
        if (node == n - 1) {
          return dp[node] = 0;
        }
        if (vis[node] == 1) {
          return -1;
        }
        else if (vis[node] == 2) {
          return dp[node];
        }
        vis[node] = 1;
        int val = 0;
        for (auto x : adj[node]) {
          val = Dfs(x.first);
          if (val != -1) {
            val += x.second;
          }
        }
        vis[node] = 2;
        return dp[node] = val;
      };
      // maximize the minimum
      for (int i = 0 ; i < (int)adj[0].size() ; i++) {
        int cur = Dfs(adj[0][i].first);
        if (cur > -1) {
          s.push_back(cur);
        }
        d.push_back(adj[0][i].second);
      }
      sort(s.begin() , s.end());
      sort(d.begin() , d.end());
    }
    auto Get = [&]() {
      int val = (int)1e9;
      for (int i = 0 ; i < (int)s.size() ; i += 1) {
        val = min(val , s[i] + d[(int)s.size() - 1 - i]);
      }
      return val;
    };
    int res = Get();
    reverse(s.begin() , s.end());
    reverse(d.begin() , d.end());
    res = max(res , Get());
    return res;
  }
  else {
    const int INF = (int)1e9;
    vector<int> dest(n , INF);
    #define pi pair<int , int>
    priority_queue<pi , vector<pi> , greater<pi>> pq;
    dest[0] = 0;
    pq.emplace(dest[0] , 0);
    while (!pq.empty()) {
      auto X = pq.top();
      pq.pop();
      if (X.first != dest[X.second]) continue;
      for (auto x :  adj[X.second]) {
        if (dest[x.first] > X.first + mx[X.second]) {
          dest[x.first] = X.first + mx[X.second];
          pq.emplace(dest[x.first] , x.first);
        }
      }
    }
    int res = dest[n - 1];
    return res;
  }
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n , m;
  cin >> n >> m;
  vector<int> a(m) , b(m) , c(m);
  for (int i = 0 ; i < m ; i += 1) {
    cin >> a[i] >> b[i] >> c[i];
  }
  cout << ferries(n , m , a , b , c) << '\n';
}

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