Submission #600904

#	Time	Username	Problem	Language	Result	Execution time	Memory
600904		narvalo	Ferries (NOI13_ferries)	C++17	17 / 40	113 ms	21200 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;

  if ((int)s.size() == (int)d.size() && (int)s.size() == n - 2) {
    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;
}

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