Submission #906621

#	Time	Username	Problem	Language	Result	Execution time	Memory
906621		duckindog	Beads and wires (APIO14_beads)	C++14	0 / 100	2 ms	5980 KiB

beads

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

using namespace std;

#define int long long

using pii = pair<int, int>;
const int N = 2e5 + 10;
int n;
vector<pii> ad[N];

int f[N][2];
void dfs(int u, int pre = 0) {
  int sacrifice = -1e9, none = -1e9;
  vector<pii> best;
  best.push_back({-1, 0});
  best.push_back({-1, 0});



  for (auto duck : ad[u]) {
    int v, w; tie(v, w) = duck;
    if (v == pre) continue;
    dfs(v, u);
    sacrifice = max(0ll, sacrifice);
    if (f[v][1] > 0) {

      sacrifice += f[v][1] + w;
      none = max(none, f[v][0] - f[v][1]);

    } else none = max(none, f[v][0] + w);

    best.push_back({v, w});

  }

  f[u][1] = max({sacrifice, sacrifice + none, -1ll});

  sort(best.begin(), best.end(), [&](pii a, pii b) {
    int x = a.first, y = b.first;

    if (x == -1) return false;
    if (y == -1) return true;
    return make_pair(f[x][0] - f[x][1], a.second) > make_pair(f[y][0] - f[y][1], b.second);
  });

  pii a, b; a = best[0], b = best[1];

  if (b.first > 0) f[u][0] = f[a.first][0] + f[b.first][0] + a.second + b.second;

  int zeoh = 0;

  for (auto duck : ad[u]) {
    int v, w; tie(v, w) = duck;
    if (v == pre) continue;
    if (v != a.first && v != b.first && f[v][1] > 0) f[u][0] += f[v][1] + w;

    if (f[v][1] > 0) zeoh += f[v][1] + w;
  }
  f[u][0] = max(f[u][0], zeoh);

}

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});
  }
  dfs(1);
  cout << f[1][0];




}

Compilation message (stderr)

beads.cpp: In function 'int32_t main()':
beads.cpp:69:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   69 |     freopen("duck.inp", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
beads.cpp:70:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   70 |     freopen("duck.out", "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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