Submission #1082988

#	Time	Username	Problem	Language	Result	Execution time	Memory
1082988		avighna	Aesthetic (NOI20_aesthetic)	C++17	100 / 100	359 ms	65764 KiB

Aesthetic

#include <bits/stdc++.h>

typedef long long ll;

struct To {
  ll v, w;
  ll i;
};

struct Edge {
  ll u, v, w;
};

const ll inf = 1e15;

int main() {
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(nullptr);

  ll n, m;
  std::cin >> n >> m;
  std::vector<std::vector<To>> adj(n + 1);
  std::vector<Edge> edges;
  ll max_w = 0;
  for (ll i = 0, u, v, w; i < m; ++i) {
    std::cin >> u >> v >> w;
    max_w = std::max(max_w, w);
    adj[u].push_back({v, w, i});
    adj[v].push_back({u, w, i});
    edges.push_back({u, v, w});
  }

  auto sssp = [&](ll node) {
    std::vector<ll> ans(n + 1, inf);
    std::vector<bool> vis(n + 1);
    std::priority_queue<std::pair<ll, ll>> pq;
    ans[node] = 0;
    pq.push({0, node});
    while (!pq.empty()) {
      auto [d, node] = pq.top();
      d *= -1;
      pq.pop();
      if (vis[node]) {
        continue;
      }
      vis[node] = true;
      for (auto [ch, w, cur_i] : adj[node]) {
        if (ans[ch] > d + w) {
          ans[ch] = d + w;
          pq.push({-ans[ch], ch});
        }
      }
    }
    return ans;
  };

  auto sssp1 = sssp(1);
  auto ssspn = sssp(n);

  std::vector<bool> active_edge(m), is_bridge(m), vis(n + 1), enc(n + 1);
  std::vector<ll> low(n + 1), tin(n + 1);

  auto check = [&](ll x) {
    for (ll i = 0; i < m; ++i) {
      auto [u, v, w] = edges[i];
      active_edge[i] =
          sssp1[u] + w + ssspn[v] <= x or sssp1[v] + w + ssspn[u] <= x;
    }
    vis.assign(n + 1, false);
    enc.assign(n + 1, false);
    enc[n] = true;
    ll timer = 0;
    std::function<void(ll, ll)> dfs;
    dfs = [&](ll node, ll par) {
      if (vis[node]) {
        return;
      }
      vis[node] = true;
      tin[node] = timer++;
      low[node] = tin[node];
      for (auto &[ch, w, i] : adj[node]) {
        if (ch == par or !active_edge[i]) {
          continue;
        }
        if (!vis[ch]) {
          dfs(ch, node);
          enc[node] = enc[node] || enc[ch];
        }
        is_bridge[i] = low[ch] > tin[node] and enc[ch];
        low[node] = std::min(low[node], low[ch]);
      }
    };
    dfs(1, 0);
    ll worst_road = edges[m - 1].w;
    for (ll i = m - 2; i >= 0; --i) {
      auto [u, v, w] = edges[i];
      if (is_bridge[i] and
          std::min(sssp1[u] + ssspn[v], sssp1[v] + ssspn[u]) + w + worst_road >
              x) {
        return true;
      }
      worst_road = std::max(worst_road, edges[i].w);
    }
    return false;
  };

  ll s = sssp1[n], e = sssp1[n] + max_w;
  while (s < e) {
    ll m = s + (e - s) / 2;
    if (check(m)) {
      s = m + 1;
    } else {
      e = m;
    }
  }
  std::cout << s << '\n';
}

• Subtask 1: 5 / 5
• Subtask 2: 8 / 8
• Subtask 3: 7 / 7
• Subtask 4: 15 / 15
• Subtask 5: 16 / 16
• Subtask 6: 22 / 22
• Subtask 7: 27 / 27