Submission #939805

#	Time	Username	Problem	Language	Result	Execution time	Memory
939805		duckindog	Race (IOI11_race)	C++17	0 / 100	4 ms	13660 KiB

race

#include<bits/stdc++.h>

using namespace std;

#ifndef LOCAL
#include "race.h"
#endif

const int N = 200'000 + 10;
int n, k;
vector<pair<int, int>> ad[N];
int answer = 1e7;

int tsz;
int sz[N];
bool mk[N];

void dfs1(int u, int pre = -1) { 
  sz[u] = 1;
  for (const auto& [v, w] : ad[u]) { 
    if (v == pre || mk[v]) continue;
    dfs1(v, u);
    sz[u] += sz[v];
  }
  tsz = sz[u];
}

int dfs2(int u, int pre = -1) { 
  for (const auto& [v, w] : ad[u]) { 
    if (v == pre || mk[v]) continue;
    if (sz[v] > tsz / 2) return dfs2(v, u);
  }
  return u;
}

int f[1'000'010];
vector<pair<int, int>> lst;
vector<int> undo;

void clr() { 
  for (const auto& i : undo) if (i <= k) f[i] = 1e7;
  f[0] = 0;
  undo.clear();
}

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

void dfs4(int u) { 
  dfs1(u, -1);
  mk[u = dfs2(u, -1)] = true;
  clr();
  
  for (const auto& [v, w] : ad[u]) { 
    if (mk[v]) continue;
    lst.clear(); dfs3(v, u, 1, w);
    for (const auto& [d, sw] : lst) if (sw <= k) answer = min(answer, d + f[k - sw]);
    for (const auto& [d, sw] : lst) if (sw <= k) f[sw] = min(f[sw], d);
  }
  
  for (const auto& [v, w] : ad[u]) if (!mk[v]) dfs4(v);
}

int best_path(int a, int b, int h[][2], int l[]) { 
  n = a; k = b;
  for (int i = 0; i < n; ++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});
  }
  memset(f, 40, sizeof f);
  dfs4(0);
  return answer > n ? -1 : answer;
}

#ifdef LOCAL
int h[N][2], l[N];
int32_t main() { 
  cin.tie(0)->sync_with_stdio(0);

  cin >> n >> k;
  for (int i = 0; i < n - 1; ++i) cin >> h[i][0] >> h[i][1] >> l[i];
  cout << best_path(n, k, h, l) << "\n";
}
#endif

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