oj.uz

Submission #1084719

# Submission time Handle Problem Language Result Execution time Memory
1084719 2024-09-06T18:25:12 Z avighna Firefighting (NOI20_firefighting) C++17
100 / 100
 212 ms 51652 KB 
#include <bits/stdc++.h>

typedef long long ll;

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

  ll n, k;
  std::cin >> n >> k;
  std::vector<std::vector<std::pair<ll, ll>>> adj(n + 1);
  for (ll i = 0, u, v, w; i < n - 1; ++i) {
    std::cin >> u >> v >> w;
    adj[u].push_back({v, w});
    adj[v].push_back({u, w});
  }

  std::vector<ll> ans;
  std::function<std::pair<bool, ll>(ll, ll, ll)> dfs;
  dfs = [&](ll x, ll par, ll parent_edge) {
    ll furthest_unprotected = 0;
    ll station_reachability = -1e15;

    for (auto &[to, w] : adj[x]) {
      if (to == par) {
        continue;
      }
      auto res = dfs(to, x, w);
      if (res.first) {
        station_reachability = std::max(station_reachability, res.second);
      } else {
        furthest_unprotected = std::max(furthest_unprotected, res.second);
      }
    }

    std::pair<bool, ll> ret;
    if (station_reachability >= furthest_unprotected) {
      // We cover everything in the subtree
      ret = {true, station_reachability - parent_edge};
    } else {
      // Okay, let's update the furthest node
      ret = {false, furthest_unprotected + parent_edge};
    }

    if (!ret.first and ret.second > k) {
      // If x => par[x] makes a node unreachable from anything outside x's
      // subtree, then x is a forced pick.
      ans.push_back(x);
      ret = {true, k - parent_edge};
    }

    // If this happens, we aren't protecting anything anymore. At the same time,
    // we have still protected everything in our subtree.
    if (ret.first and ret.second < 0) {
      ret = {false, 0};
    }
    return ret;
  };
  // The reason we're making the parent edge very large is because by default
  // our algorithm tries to get the parent to place down a fire station if the
  // distance is small enough, since this is optimal. However, in the case of 1,
  // we have no parent, so this would behave as if there was a large barrier
  // between 1 and its parent, forcing a placemenet (if necessary) at 1 itself.
  dfs(1, 0, 1e15);

  std::cout << ans.size() << '\n';
  for (auto &i : ans) {
    std::cout << i << ' ';
  }
  std::cout << '\n';
}

Subtask #1
3.0 / 3.0

# Verdict Execution time Memory Grader output
1 Correct 174 ms 34824 KB Output is correct
2 Correct 159 ms 34752 KB Output is correct
3 Correct 51 ms 12996 KB Output is correct
4 Correct 152 ms 33700 KB Output is correct
5 Correct 0 ms 348 KB Output is correct
6 Correct 0 ms 348 KB Output is correct

Subtask #2
5.0 / 5.0

# Verdict Execution time Memory Grader output
1 Correct 0 ms 344 KB Output is correct
2 Correct 0 ms 348 KB Output is correct
3 Correct 1 ms 456 KB Output is correct
4 Correct 0 ms 348 KB Output is correct
5 Correct 0 ms 348 KB Output is correct
6 Correct 0 ms 348 KB Output is correct
7 Correct 1 ms 348 KB Output is correct
8 Correct 0 ms 348 KB Output is correct
9 Correct 0 ms 348 KB Output is correct
10 Correct 0 ms 348 KB Output is correct
11 Correct 1 ms 348 KB Output is correct
12 Correct 0 ms 604 KB Output is correct
13 Correct 0 ms 348 KB Output is correct
14 Correct 0 ms 348 KB Output is correct
15 Correct 0 ms 348 KB Output is correct

Subtask #3
9.0 / 9.0

# Verdict Execution time Memory Grader output
1 Correct 0 ms 344 KB Output is correct
2 Correct 1 ms 348 KB Output is correct
3 Correct 0 ms 348 KB Output is correct
4 Correct 0 ms 348 KB Output is correct
5 Correct 1 ms 348 KB Output is correct
6 Correct 0 ms 348 KB Output is correct
7 Correct 1 ms 348 KB Output is correct
8 Correct 0 ms 348 KB Output is correct
9 Correct 0 ms 348 KB Output is correct
10 Correct 0 ms 348 KB Output is correct
11 Correct 1 ms 344 KB Output is correct
12 Correct 0 ms 348 KB Output is correct
13 Correct 0 ms 348 KB Output is correct
14 Correct 0 ms 348 KB Output is correct
15 Correct 0 ms 348 KB Output is correct
16 Correct 0 ms 348 KB Output is correct
17 Correct 0 ms 348 KB Output is correct
18 Correct 0 ms 348 KB Output is correct
19 Correct 0 ms 348 KB Output is correct
20 Correct 0 ms 348 KB Output is correct
21 Correct 0 ms 348 KB Output is correct
22 Correct 0 ms 348 KB Output is correct
23 Correct 0 ms 348 KB Output is correct
24 Correct 1 ms 348 KB Output is correct
25 Correct 0 ms 348 KB Output is correct
26 Correct 0 ms 348 KB Output is correct

Subtask #4
19.0 / 19.0

# Verdict Execution time Memory Grader output
1 Correct 189 ms 34616 KB Output is correct
2 Correct 66 ms 17360 KB Output is correct
3 Correct 72 ms 17872 KB Output is correct
4 Correct 57 ms 15564 KB Output is correct
5 Correct 0 ms 348 KB Output is correct
6 Correct 0 ms 452 KB Output is correct
7 Correct 116 ms 30988 KB Output is correct
8 Correct 120 ms 30904 KB Output is correct
9 Correct 136 ms 31168 KB Output is correct
10 Correct 121 ms 31168 KB Output is correct
11 Correct 184 ms 34648 KB Output is correct
12 Correct 110 ms 21428 KB Output is correct
13 Correct 59 ms 13388 KB Output is correct
14 Correct 113 ms 20072 KB Output is correct
15 Correct 132 ms 24260 KB Output is correct
16 Correct 105 ms 26064 KB Output is correct
17 Correct 93 ms 21836 KB Output is correct
18 Correct 89 ms 21372 KB Output is correct

Subtask #5
26.0 / 26.0

# Verdict Execution time Memory Grader output
1 Correct 1 ms 476 KB Output is correct
2 Correct 1 ms 600 KB Output is correct
3 Correct 1 ms 352 KB Output is correct
4 Correct 1 ms 604 KB Output is correct
5 Correct 2 ms 860 KB Output is correct
6 Correct 1 ms 720 KB Output is correct
7 Correct 2 ms 936 KB Output is correct
8 Correct 2 ms 860 KB Output is correct
9 Correct 1 ms 632 KB Output is correct
10 Correct 2 ms 860 KB Output is correct
11 Correct 2 ms 684 KB Output is correct
12 Correct 1 ms 600 KB Output is correct
13 Correct 1 ms 860 KB Output is correct
14 Correct 2 ms 856 KB Output is correct
15 Correct 1 ms 604 KB Output is correct
16 Correct 1 ms 604 KB Output is correct
17 Correct 1 ms 604 KB Output is correct
18 Correct 1 ms 604 KB Output is correct
19 Correct 1 ms 604 KB Output is correct
20 Correct 1 ms 604 KB Output is correct
21 Correct 1 ms 636 KB Output is correct

Subtask #6
38.0 / 38.0

# Verdict Execution time Memory Grader output
1 Correct 126 ms 29456 KB Output is correct
2 Correct 117 ms 27728 KB Output is correct
3 Correct 138 ms 29896 KB Output is correct
4 Correct 59 ms 14152 KB Output is correct
5 Correct 183 ms 45240 KB Output is correct
6 Correct 212 ms 43180 KB Output is correct
7 Correct 164 ms 49284 KB Output is correct
8 Correct 159 ms 47816 KB Output is correct
9 Correct 141 ms 40652 KB Output is correct
10 Correct 164 ms 39368 KB Output is correct
11 Correct 158 ms 51652 KB Output is correct
12 Correct 82 ms 20304 KB Output is correct
13 Correct 151 ms 42440 KB Output is correct
14 Correct 157 ms 37964 KB Output is correct
15 Correct 124 ms 30292 KB Output is correct
16 Correct 121 ms 28500 KB Output is correct
17 Correct 117 ms 28144 KB Output is correct
18 Correct 138 ms 30144 KB Output is correct
19 Correct 82 ms 21072 KB Output is correct
20 Correct 49 ms 12116 KB Output is correct
21 Correct 139 ms 30176 KB Output is correct