Submission #907427

#	Time	Username	Problem	Language	Result	Execution time	Memory
907427		duckindog	Beads and wires (APIO14_beads)	C++14	0 / 100	2 ms	4956 KiB

beads

// from duckindog wth depression
#include<bits/stdc++.h>

using namespace std;

#define int long long

const int N = 1e5 + 10,
          M = -1e15;
int n;
vector<pair<int, int>> ad[N];

int f[N][3];
void dfs(int u, int pre = 0) {

  int all = M, none = M;
  int s = 0;
  vector<int> best;
  map<int, int> rvs;
  for (auto duck : ad[u]) {
    int v, w; tie(v, w) = duck;
    if (v == pre) continue;
    dfs(v, u);

    int x = f[v][0], y = f[v][1];
    all = max(0ll, all);
    if (x > 0) {
      all += max(x + w, y);
      none = max(none, y - (x + w > y ? x : y));
    } else none = max(none, y + w);

    f[u][1] += max({0ll, f[v][1], f[v][0] + w});
    rvs[v] = best.size();
    best.push_back(max(f[v][0] + w, 0ll));
  }
  f[u][0] = max(M, all + none);
  for (int i = 1; i < best.size(); ++i) best[i] += best[i - 1];

  f[u][2] = M;
  for (auto duck : ad[u]) {
    int v, w; tie(v, w) = duck;
    int p = rvs[v];
    int lt = !p ? 0 : best[p - 1];
    for (auto chik : ad[u]) {
      int _v, _w; tie(_v, _w) = chik;
      int _p = rvs[_v];
      if (_p <= p) continue;
      int rt = best[best.size() - 1] - best[_p];
      f[u][2] = max(f[u][2], lt + rt + max(f[v][2] + f[_v][1], f[v][1] + f[_v][2]));
    }
  }

}

int32_t main() {
  cin.tie(0)->sync_with_stdio(0);

  if (fopen("duck.inp", "r")) {
    freopen("duck.inp", "r", stdin);
    freopen("duck.out", "w", stdout);
  }

  cin >> n;
  for (int i = 1; i < n; ++i) {
    int u, v, w; cin >> u >> v >> w;
    ad[u].push_back({v, w});
    ad[v].push_back({u, w});
  }

  int answer = 0;
  for (int i = 1; i <= n; ++i) {
    memset(f, 0, sizeof f);
    f[0][0] = f[0][1] = f[0][2] = M;
    dfs(i);

    for (int j = 1; j <= n; ++j) answer = max({answer, f[j][1], f[j][2]});
  }
  cout << answer;
}

Compilation message (stderr)

beads.cpp: In function 'void dfs(long long int, long long int)':
beads.cpp:37:21: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   37 |   for (int i = 1; i < best.size(); ++i) best[i] += best[i - 1];
      |                   ~~^~~~~~~~~~~~~
beads.cpp:17:7: warning: unused variable 's' [-Wunused-variable]
   17 |   int s = 0;
      |       ^
beads.cpp: In function 'int32_t main()':
beads.cpp:59:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   59 |     freopen("duck.inp", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
beads.cpp:60:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   60 |     freopen("duck.out", "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 13
• Subtask 2: 0 / 15
• Subtask 3: 0 / 29
• Subtask 4: 0 / 43