Submission #1108190

#	Time	Username	Problem	Language	Result	Execution time	Memory
1108190		keunbum	Race (IOI11_race)	C++17	100 / 100	238 ms	32584 KiB

race

#include <bits/stdc++.h>

using namespace std;

#ifdef LOCAL
#include "debug.h"
#else
#define debug(...)
#endif

int best_path(int N, int K, int H[][2], int L[]) {
  int n = N;
  int k = K;
  vector<vector<pair<int, int>>> g(n);
  for (int i = 0; i < n - 1; ++i) {
    int x = H[i][0];
    int y = H[i][1];
    int z = L[i];
    g[x].emplace_back(y, z);
    g[y].emplace_back(x, z);
  }
  vector<bool> removed(n, false);
  vector<int> sz(n);
  vector<int> pv(n);
  auto DFS = [&](auto&& self, int v) -> void {
    sz[v] = 1;
    for (auto [u, _] : g[v]) {
      if (u != pv[v] && !removed[u]) {
        pv[u] = v;
        self(self, u);
        sz[v] += sz[u];
      }
    }
  };
  auto GetCenter = [&](int r) {
    pv[r] = -1;
    DFS(DFS, r);
    int tot = sz[r];
    while (true) {
      int nr = -1;
      for (auto [u, _] : g[r]) {
        if (u != pv[r] && !removed[u] && sz[u] * 2 > tot) {
          nr = u;
          break;
        }
      }
      if (nr == -1) {
        return r;
      }
      r = nr;
    }
  };
  int ans = n;
  int iter = 0;
  vector<int> aux(k + 1, 0);
  vector<int> dp(k + 1, 0);
  auto Find = [&](auto&& self, int v, int pv, int dist, int depth) -> void {
    if (dist > k) {
      return;
    }
    if (aux[k - dist] == iter) {
      ans = min(ans, dp[k - dist] + depth);
    }
    if (dist == k) {
      ans = min(ans, depth);
    }
    for (auto [u, w] : g[v]) {
      if (!removed[u] && u != pv) {
        self(self, u, v, dist + w, depth + 1);
      }
    }
  };
  auto Calc = [&](auto&& self, int v, int pv, int dist, int depth) -> void {
    if (dist > k) {
      return;
    }
    if (aux[dist] < iter) {
      aux[dist] = iter;
      dp[dist] = depth;
    } else
    if (dp[dist] > depth) {
      aux[dist] = iter;
      dp[dist] = depth;
    }
    for (auto [u, w] : g[v]) {
      if (!removed[u] && u != pv) {
        self(self, u, v, dist + w, depth + 1);
      }
    }
  };  
  auto Solve = [&](auto&& self, int v) -> void {
    v = GetCenter(v);
    iter += 1;
    for (auto [u, w] : g[v]) {
      if (!removed[u]) {
        Find(Find, u, v, w, 1);
        Calc(Calc, u, v, w, 1);
      }
    }
    removed[v] = true;
    for (auto [u, _] : g[v]) {
      if (!removed[u]) {
        self(self, u);
      }
    }
  };
  Solve(Solve, 0);
  return (ans == n ? -1 : ans);
}

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