Submission #201644

#	Time	Username	Problem	Language	Result	Execution time	Memory
201644		waynetuinfor	Olympic Bus (JOI20_ho_t4)	C++17	100 / 100	418 ms	2168 KiB

ho_t4

#include <algorithm>
#include <array>
#include <iostream>
#include <queue>
#include <vector>

int main() {
  int n, m;
  std::cin >> n >> m;
  constexpr int kInf = 1'000'000'000;
  std::vector<std::vector<int>> dist(n, std::vector<int>(n, kInf));
  for (int i = 0; i < n; ++i) dist[i][i] = 0;
  std::vector<std::array<int, 4>> ed(m);
  std::vector<std::vector<std::pair<int, int>>> g(n);
  for (int i = 0; i < m; ++i) {
    int u, v, c, d;
    std::cin >> u >> v >> c >> d;
    u--, v--;
    dist[u][v] = std::min(dist[u][v], c);
    ed[i] = {u, v, c, d};
    g[u].emplace_back(v, i);
  }
  for (int k = 0; k < n; ++k) {
    for (int i = 0; i < n; ++i) {
      for (int j = 0; j < n; ++j) {
        dist[i][j] = std::min(dist[i][j], dist[i][k] + dist[k][j]);
      }
    }
  }
  int64_t ans = dist[0][n - 1] + dist[n - 1][0];

  auto Dijkstra = [&](int s, int e, int v) {
    std::vector<int> dist(n, kInf), used(n);
    std::priority_queue<std::pair<int, int>> pq;
    pq.emplace(0, s);
    dist[s] = 0;
    while (!pq.empty()) {
      int x = pq.top().second;
      pq.pop();
      if (x == e) break;
      if (used[x]++) continue;
      for (auto i : g[x]) {
        int u = i.first, z = i.second;
        if (z == v) continue;
        if (dist[u] > dist[x] + ed[z][2]) {
          dist[u] = dist[x] + ed[z][2];
          pq.emplace(-dist[u], u);
        }
      }
      if (x == ed[v][1]) {
        if (dist[ed[v][0]] > dist[x] + ed[v][2]) {
          dist[ed[v][0]] = dist[x] + ed[v][2];
          pq.emplace(-dist[ed[v][0]], ed[v][0]);
        }
      }
    }
    return dist[e];
  };

  for (int i = 0; i < m; ++i) {
    int u = ed[i][0], v = ed[i][1], c = ed[i][2], d = ed[i][3];
    int64_t a = std::min(dist[0][n - 1], dist[0][v] + dist[u][n - 1] + c);
    int64_t b = std::min(dist[n - 1][0], dist[n - 1][v] + dist[u][0] + c);
    if (a + b + d < ans) {
      int64_t x = Dijkstra(0, n - 1, i);
      int64_t y = Dijkstra(n - 1, 0, i);
      ans = std::min(ans, x + y + d);
    }
  }
  if (ans >= kInf) ans = -1;
  std::cout << ans << "\n";
  return 0;
}

• Subtask 1: 5 / 5
• Subtask 2: 11 / 11
• Subtask 3: 21 / 21
• Subtask 4: 63 / 63