Submission #980587

#	Time	Username	Problem	Language	Result	Execution time	Memory
980587		hieptk	Race (IOI11_race)	C++17	0 / 100	2 ms	9052 KiB

race

#include <iostream>
#include <vector>
#include <cmath>
#include <numeric>
#include <algorithm>
#include <set>
#include <unordered_set>
#include <cstring>
#include <unordered_map>
#include <iomanip>
#include <queue>
#include <map>
#include <sstream>
#include <stack>
#include <bitset>
 
using ll = long long;
using ld = long double;
 
using namespace std;

const int nm = 200002;
const ll inf = 1e18;

vector<pair<int, ll>> adj[nm];
int H[nm][2], L[nm];
int Res;
bool deleted[nm];

void bfs(int i, int n, int k) {
  // cout << "bfs " << i << " " << n << " " << k << "\n";
  queue<int> q;
  q.push(i);
  vector<pair<ll, ll>> d(n, {inf, inf});
  d[i] = {0, 0};
  while (q.size()) {
    int i = q.front();
    q.pop();
    for (auto [j, w]: adj[i]) {
      if (deleted[j]) continue;
      if (d[j].second > d[i].second + 1) {
        d[j].first = d[i].first + w;
        d[j].second = d[i].second + 1;
        if (d[j].second < Res && d[j].first < k) q.push(j);
      }
    }
  }

  unordered_map<ll, int> best;
  for (int j = 0; j < n; ++j) {
    if (d[j].first == inf) continue;
    if (d[j].first == k) Res = min(Res, (int) d[j].second);
    else if (best.count(k - d[j].first)) {
      Res = min(Res, (int) d[j].second + best[k - d[j].first]);
    }

    if (best.count(d[j].first)) best[d[j].first] = min(best[d[j].first], (int) d[j].second);
    else best[d[j].first] = d[j].second;
  }
}

void dfs(int i, int p, vector<int> &nchild, vector<int> &maxchild) {
  nchild[i] = 1;
  for (auto [j, w]: adj[i]) {
    if (j == p || deleted[j]) continue;
    dfs(j, i, nchild, maxchild);
    nchild[i] += nchild[j];
    maxchild[i] = max(maxchild[i], nchild[j]);
  }
}

int findCenter(int root, int n) {
  vector<int> nchild(n), maxchild(n);
  dfs(root, -1, nchild, maxchild);
  int s = nchild[root];
  if (s == 1) return -1;
  for (int i = 0; i < n; ++i) {
    if (nchild[i] > 0) {
      int maxsplit = max(maxchild[i], s - nchild[i]);
      if (maxsplit <= s / 2) return i;
    }
  }
  return -1;
}

void calc(int root, int n, int k) {
  int u = findCenter(root, n);
  // cout << "root " << root << " center " << u << "\n";
  if (u == -1) return;
  bfs(u, n, k);
  // cout << "root " << root << " center " << u << " " << Res << "\n";
  deleted[u] = 1;
  for (auto [j, w]: adj[u]) {
    if (!deleted[j]) calc(j, n, k);
  }
}

int best_path(int n, int k, int H[][2], int L[]) {
    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]);
    }
    memset(deleted, 0, sizeof(deleted));
    Res = n + 1;
    calc(0, n, k);
    return Res < n ? Res : -1;
}
 
// int main() {
//     #ifdef LOCAL
//     freopen("input.txt", "r", stdin);
//     #endif
//     ios::sync_with_stdio(0);
//     cin.tie(0);
//     int n, k;
//     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";
// }

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