Submission #907421

#	Time	Username	Problem	Language	Result	Execution time	Memory
907421		duckindog	Beads and wires (APIO14_beads)	C++14	13 / 100	8 ms	5156 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) {

  vector<pair<int, int>> best;
  int all = M, none = M;
  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);

    best.push_back({v, w});
  }
  f[u][0] = max(M, all + none);

  using pii = pair<int, int>;
  best.push_back({0, M});
  best.push_back({0, M});

  sort(best.begin(), best.end(), [&](pii a, pii b) {
    int x = max(f[a.first][1], f[a.first][2]) + a.second;
    int y = max(f[b.first][1], f[b.first][2]) + b.second;

    return x - max(0ll, f[a.first][0] + a.second) >
            y - max(0ll, f[b.first][0] + b.second);
  });

  auto fi = best[0], se = best[1];
  if (f[fi.first][2] < f[se.first][2]) swap(fi, se);
  f[u][2] = f[fi.first][2] + fi.second
              + f[se.first][1] + se.second;
  f[u][2] = max(f[u][2], f[fi.first][1] + fi.second + f[se.first][1] + se.second);

  f[u][2] = max(M, f[u][2]);

  for (auto duck : ad[u]) {
    int v, w; tie(v, w) = duck;
    if (v == pre) continue;


    if (v != fi.first && v != se.first && f[u][2] != M)
      f[u][2] += max(0ll, f[v][0] + w);

    f[u][1] += max({0ll, f[v][1], f[v][0] + w});

  }

}

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 'int32_t main()':
beads.cpp:72:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   72 |     freopen("duck.inp", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
beads.cpp:73:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   73 |     freopen("duck.out", "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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