Submission #971248

#	Time	Username	Problem	Language	Result	Execution time	Memory
971248		kilkuwu	Beads and wires (APIO14_beads)	C++17	100 / 100	135 ms	24892 KiB

beads

#include <bits/stdc++.h>

#define nl '\n'

#ifdef LOCAL
#include "template/debug.hpp"
#else
#define dbg(...) ;
#define timer(...) ;
#endif

const int mxN = 2e5 + 5;
int dp[mxN][2][2], up[mxN];
std::vector<std::pair<int, int>> adj[mxN];
int N;

int dfs(int u, int p, int e, int b) {
  if (dp[u][e][b] != -1) return dp[u][e][b];
  std::vector<int> child;
  for (auto [v, c] : adj[u]) {
    if (v == p) continue;
    up[v] = c;
    child.push_back(v);
    dfs(v, u, 0, 0);  
    dfs(v, u, 0, 1);  
    dfs(v, u, 1, 0);  
    dfs(v, u, 1, 1);  
  }

  int& ans = dp[u][e][b];
  int sum_e_no_b = 0;
  for (int v : child) {
    sum_e_no_b += dp[v][1][0];
  }
  ans = sum_e_no_b;

  if (b) {
    for (int v : child) {
      ans = std::max(ans, sum_e_no_b - dp[v][1][0] + dp[v][1][1]);
    }

    if (child.size() >= 2) {
      std::sort(child.begin(), child.end(), [&](int i, int j) {
        return dp[i][0][0] + up[i] - dp[i][1][0] >
               dp[j][0][0] + up[j] - dp[j][1][0];
      });

      for (int v : child) {
        int cand = sum_e_no_b - dp[v][1][0] + dp[v][0][1] + up[v];
        int vv = child[0] == v ? child[1] : child[0];
        cand += dp[vv][0][0] + up[vv] - dp[vv][1][0];
        ans = std::max(ans, cand);
      }
    }
  }

  if (e) {
    for (int v : child) {
      int cand = sum_e_no_b + up[u] + up[v] + dp[v][0][b] - dp[v][1][0];
      ans = std::max(ans, cand);
    }
  }

  return ans;
}

signed main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);

  memset(dp, -1, sizeof(dp));
  std::cin >> N;
  for (int i = 0; i + 1 < N; i++) {
    int u, v, c;
    std::cin >> u >> v >> c;
    --u, --v;
    adj[u].emplace_back(v, c);
    adj[v].emplace_back(u, c);
  }
  std::cout << dfs(0, 0, 0, 1) << nl;
}

/*
10
4 10 2
1 2 21
1 3 13
6 7 1
7 9 5
2 4 3
2 5 8
1 6 55
6 8 34
*/

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