Submission #939779

#	Time	Username	Problem	Language	Result	Execution time	Memory
939779		duckindog	Race (IOI11_race)	C++17	0 / 100	2 ms	9560 KiB

race

#include<bits/stdc++.h>
#include "race.h"

using namespace std;

const int N = 2e5 + 10;

int total_sz, wei, answer;
bool marked[N];
int sz[N];
vector<pair<int, int>> ad[N];

void dfs1(int u, int p) {
  sz[u] = 1;
  total_sz += 1;
  for (const auto& [v, w] : ad[u]) {
    if (marked[v] || v == p) continue;
    dfs1(v, u);
    sz[u] += sz[v];
  }
}

int dfs2(int u, int p) {
  for (const auto& [v, w] : ad[u]) {
    if (marked[v] || v == p) continue;
    if (sz[v] > total_sz / 2) return dfs2(v, u);
  }
  return u;
}

int f[N];
vector<int> undo;
vector<pair<int, int>> lst;

void dfs3(int u, int p, int d, int tw) {
  lst.push_back({d, tw});
  undo.push_back(d);
  for (const auto& [v, w] : ad[u]) {
    if (v == p || marked[v]) continue;
    dfs3(v, u, d + 1, tw + w);
  }
}

void dfs4(int u) {
  total_sz = 0;
  dfs1(u, -1);
  marked[u = dfs2(u, -1)] = true;

  f[0] = 0;
  for (const auto& [v, w] : ad[u]) {
    dfs3(v, u, 1, w);

    for (const auto& [d, tw] : lst) {
      if (tw > wei) continue;
      answer = min(answer, d + f[wei - tw]);
    }

    for (const auto& [d, tw] : lst) {
      if (tw > wei) continue;
      f[d] = min(f[d], tw);
    }

    lst.clear();
  }

  for (const auto& i : undo) f[i] = 1e7;
  undo.clear();

  for (const auto& [v, w] : ad[u]) {
    if (marked[v]) continue;
    dfs4(v);
  }
}

int best_path(int n, int k, int h[][2], int l[]) { 
  for (int i = 0; i < n - 1; ++i) { 
    int u = h[i][0], v = h[i][1], w = l[i];
    ad[u].push_back({v, w});
    ad[v].push_back({u, w});
  }
  answer = 1e7; wei = k;
  memset(f, 40, sizeof f); 
  dfs4(0);
  return answer > n ? -1 : answer;
} 

#ifdef LOCAL
#define MAX_AA 500000
static int AA, K;
static int H[MAX_AA][2];
static int L[MAX_AA];
static int solution;
 
#define int long long
mt19937_64 rng(8384815663);
int rnd(int l, int r) { return l + rng() % (r - l + 1); }
 
inline 
void my_assert(int e) {if (!e) abort();}
 
void read_input()
{
  freopen("input.txt", "r", stdin);
  // AA = rnd(2e5, 2e5), K = rnd(100, 100);
  cin >> AA >> K;
  for (int i = 0; i < AA - 1; ++i) { 
    // H[i][0] = rnd(i, i);
    // H[i][1] = i + 1;
    // L[i] = rnd(1, 100);
    cin >> H[i][0] >> H[i][1];
    cin >> L[i];
  }
  solution = -1;
  // cin >> solution;
}
 
int32_t main() {
  int ans;
  read_input();
  ans = best_path(AA,K,H,L);
  cout << ans << "\n";
 
  return 0;
}
#endif

• Subtask 1: 0 / 9
• Subtask 2: 0 / 12
• Subtask 3: 0 / 22
• Subtask 4: 0 / 57