Submission #996684

#	Time	Username	Problem	Language	Result	Execution time	Memory
996684		MilosMilutinovic	Construction Project 2 (JOI24_ho_t2)	C++14	100 / 100	294 ms	32388 KiB

Main

#include <bits/stdc++.h>

using namespace std;

template <typename T>
class fenwick {
 public:
  vector<T> fenw;
  int n;

  fenwick(int _n) : n(_n) {
    fenw.resize(n);
  }

  void modify(int x, T v) {
    while (x < n) {
      fenw[x] += v;
      x |= (x + 1);
    }
  }

  T get(int x) {
    T v{};
    while (x >= 0) {
      v += fenw[x];
      x = (x & (x + 1)) - 1;
    }
    return v;
  }
};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  int s, t, l;
  cin >> s >> t >> l;
  --s; --t;
  long long k;
  cin >> k;
  vector<vector<pair<int, int>>> g(n);
  for (int i = 0; i < m; i++) {
    int u, v, w;
    cin >> u >> v >> w;
    --u; --v;
    g[u].push_back({v, w});
    g[v].push_back({u, w});
  }
  const long long inf = (long long) 1e18;
  vector<vector<long long>> dist(2, vector<long long>(n));
  auto Dijkstra = [&](int s, vector<long long>& d) {
    d = vector<long long>(n, inf);
    d[s] = 0;
    set<pair<long long, int>> st;
    st.emplace(0, s);
    while (!st.empty()) {
      auto it = st.begin();
      int v = it->second;
      st.erase(it);
      for (auto& e : g[v]) {
        int u = e.first;
        int w = e.second;
        if (d[u] > d[v] + w) {
          if (d[u] != inf) {
            st.erase({d[u], u});
          }
          d[u] = d[v] + w;
          st.emplace(d[u], u);
        }
      }
    }
  };
  Dijkstra(s, dist[0]);
  Dijkstra(t, dist[1]);
  if (dist[0][t] <= k) {
    cout << n * 1LL * (n - 1) / 2 << '\n';
    return 0;
  }
  // dist[0][i] + L <= K - dist[1][j]
  vector<long long> xs;
  for (int i = 0; i < n; i++) {
    xs.push_back(dist[0][i] + l);
    xs.push_back(k - dist[1][i]);
  }
  sort(xs.begin(), xs.end());
  xs.erase(unique(xs.begin(), xs.end()), xs.end());
  int sz = (int) xs.size();
  fenwick<int> fenw(sz);
  long long res = 0;
  vector<int> order(n);
  iota(order.begin(), order.end(), 0);
  sort(order.begin(), order.end(), [&](int i, int j) {
    return dist[0][i] < dist[0][j];
  });
  for (int i : order) {
    res += fenw.get((int) (lower_bound(xs.begin(), xs.end(), k - dist[1][i]) - xs.begin()));
    fenw.modify((int) (lower_bound(xs.begin(), xs.end(), dist[0][i] + l) - xs.begin()), 1);
  }
  cout << res << '\n';
  return 0;
}

• Subtask 1: 8 / 8
• Subtask 2: 16 / 16
• Subtask 3: 29 / 29
• Subtask 4: 47 / 47