Submission #977638

#	Time	Username	Problem	Language	Result	Execution time	Memory
977638		Ning07	Swapping Cities (APIO20_swap)	C++17	37 / 100	2095 ms	13760 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--) 

struct dsu {
   vector<int> fa, sz;
   vector<bool> ok;
   dsu(int n) {
      fa.resize(n + 10);
      iota(fa.begin(), fa.end(), 0);
      sz.assign(n + 10, 1);
      ok.assign(n + 10, false);
   }
   int find(int x) {
      while (x != fa[x]) x = fa[x] = fa[fa[x]];
      return x;
   }
   bool merge(int x, int y) {
      int px = find(x), py = find(y);
      if (px == py) return false;
      if (sz[py] > sz[px]) swap(px, py);
      sz[px] += sz[py]; fa[py] = px;
      ok[px] = ok[px] || ok[py];
      return true;
   }
   bool same(int x, int y) {
      int px = find(x), py = find(y);
      return px == py;
   }
};

const int nax = 100050;

int N, M;
vector<pair<int, int>> G[nax];
vector<pair<int, pair<int, int>>> 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) edges.push_back(make_pair(_W[i], make_pair(_U[i], _V[i])));
   sort(edges.begin(), edges.end());
}

int getMinimumFuelCapacity(int X, int Y) {
   // in order to speed up,
   // we want to check connectivity, cycle, and whether the degree >= 3

   dsu D(N);
   vector<int> deg(N);
   for (int i = 0; i < edges.size(); i++) {
      int w = edges[i].first;
      int u = edges[i].second.first, v = edges[i].second.second;
      if (D.same(u, v)) D.ok[D.find(u)] = true; // cycle is formed
      deg[u]++; deg[v]++;
      if (deg[u] >= 3) D.ok[D.find(u)] = true; // degree >= 3
      if (deg[v] >= 3) D.ok[D.find(v)] = true; // degree >= 3
      D.merge(u, v); // merge them
      if (D.same(X, Y) && D.ok[D.find(X)] == true)  // if they are in the same component and its ok to swap them
         return w;
   }
   return -1;
}

Compilation message (stderr)

swap.cpp: In function 'int getMinimumFuelCapacity(int, int)':
swap.cpp:55:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, std::pair<int, int> > >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   55 |    for (int i = 0; i < edges.size(); i++) {
      |                    ~~^~~~~~~~~~~~~~

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