Submission #231899

#	Time	Username	Problem	Language	Result	Execution time	Memory
231899		IOrtroiii	Race (IOI11_race)	C++14	0 / 100	11 ms	8960 KiB

race

#ifndef KienVu
#include "race.h"
#endif // KienVu

#include <bits/stdc++.h>

using namespace std;

int N, K;
vector<pair<int, int>> adj[200200];
int dist[200200];
int distw[200200];
int sz[200200];
bool delt[200200];
int best[1000100];

int calc_sz(int v, int p) {
   sz[v] = 1;
   for (auto e : adj[v]) {
      int u, w; tie(u, w) = e;
      if (u != p && !delt[u]) {
         sz[v] += calc_sz(u, v);
      }
   }
   return v;
}

int centroid(int v, int p, int r) {
   for (auto e : adj[v]) {
      int u, w; tie(u, w) = e;
      if (u != p && !delt[u] && 2 * sz[u] >= sz[r]) {
         return centroid(u, v, r);
      }
   }
   return v;
}

void prepare(int v, int p, int d, int dw) {
   dw = min(dw, K + 1);
   dist[v] = d;
   distw[v] = dw;
   for (auto e : adj[v]) {
      int u, w; tie(u, w) = e;
      if (u != p && !delt[u]) {
         prepare(u, v, d + 1, dw + w);
      }
   }
}

int ans = 1e9;

void query(int v, int p) {
   if (distw[v] <= K) {
      ans = min(ans, dist[v] + best[K - distw[v]]);
   }
   for (auto e : adj[v]) {
      int u, w; tie(u, w) = e;
      if (u != p && !delt[u]) {
         query(u, v);
      }
   }
}

void modify(int v, int p) {
   if (distw[v] <= K) best[distw[v]] = min(best[distw[v]], dist[v]);
   for (auto e : adj[v]) {
      int u, w; tie(u, w) = e;
      if (u != p && !delt[u]) {
         modify(u, v);
      }
   }
}

void reset(int v, int p) {
   if (distw[v] <= K) best[distw[v]] = 1e9;
   for (auto e : adj[v]) {
      int u, w; tie(u, w) = e;
      if (u != p && !delt[u]) {
         reset(u, v);
      }
   }
}

void solve(int v) {
   calc_sz(v, -1);
   v = centroid(v, -1, v);
   prepare(v, -1, 0, 0);
   for (auto e : adj[v]) {
      int u, w; tie(u, w) = e;
      if (!delt[u]) {
         query(u, v);
         modify(u, v);
      }
   }
   reset(v, -1);
   delt[v] = true;
   for (auto e : adj[v]) if (!delt[e.first]) solve(e.first);
}

int best_path(int N, int K, int H[][2], int L[]) {
   ::N = N;
   ::K = K;
   for (int i = 0; i < N - 1; ++i) {
      adj[H[i][0]].emplace_back(H[i][1], L[i]);
      adj[H[i][1]].emplace_back(H[i][0], L[i]);
   }
   for (int i = 0; i < 1000100; ++i) best[i] = 1e9;
   solve(0);
   if (ans > N) ans = -1;
   return ans;
}

#ifdef KienVu
int main() {
   int N, K;
   while (cin >> N >> K) {
      int H[N - 1][2], L[N - 1];
      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