Submission #977629

#	Time	Username	Problem	Language	Result	Execution time	Memory
977629		Ning07	Swapping Cities (APIO20_swap)	C++17	17 / 100	2037 ms	14436 KiB

swap

#include "swap.h"

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

#define L(i, j, k) for (int i = (j); i <= k; i++) 
#define R(i, j, k) for (int i = (j); i >= k; i--) 

const int nax = 100050;

int N, M;
vector<pair<int, int>> G[nax], edges; 

void init(int _N, int _M, std::vector<int> _U, std::vector<int> _V, std::vector<int> _W) {
   N = _N; M = _M;
   L(i, 0, M - 1){
      G[_U[i]].push_back(make_pair(_V[i], i));
      G[_V[i]].push_back(make_pair(_U[i], i));
      edges.push_back(make_pair(_W[i], i));
   }
   sort(edges.begin(), edges.end());
}

int getMinimumFuelCapacity(int X, int Y) {
   // notice that either we have a node with degree >= 3
   // or that we have a cycle
   // since the answer is the maximum, why not consider adding the edge one by one?

   vector<bool> ban(M, true), vis(N);
   function<void(int, int)> dfs = [&](int u, int f) {
      vis[u] = true;
      for (auto & v : G[u]) {
         if (ban[v.second]) continue;
         if (v.first == f) continue;
         if (vis[v.first]) continue;
         dfs(v.first, f);
      }
   };
   function<bool(int, int)> cycle = [&](int u, int f) {
      vis[u] = true;
      for (auto & v : G[u]) {
         if (ban[v.second]) continue;
         if (v.first == f) continue;

         if (vis[v.first]) return true;
         if (cycle(v.first, u)) return true;
      }
      return false;
   };
   function<bool()> degree = [&]() {
      for (int i = 0; i < N; i++) {
         int deg = 0;
         if (vis[i] == true) {
            for (auto & v : G[i]) {
               deg += ban[v.second] == false;
            }
         }
         if (deg >= 3) 
            return true;
      }
      return false;
   };
   for (int i = 0; i < M; i++) {
      int w = edges[i].first;
      int id = edges[i].second;
      ban[id] = false;
      vis = vector<bool>(N);
      dfs(X, -1);
      if (vis[Y] == false) continue;
      vis = vector<bool>(N);
      if (cycle(X, -1) || degree()) {
         return w;
      }
   }
   return -1;
}

• Subtask 1: 0 / 6
• Subtask 2: 0 / 7
• Subtask 3: 17 / 17
• Subtask 4: 0 / 20
• Subtask 5: 0 / 23
• Subtask 6: 0 / 27