Submission #948330

#	Time	Username	Problem	Language	Result	Execution time	Memory
948330		NeroZein	Pastiri (COI20_pastiri)	C++17	100 / 100	761 ms	114720 KiB

pastiri

#include "bits/stdc++.h"
using namespace std;

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

const int LOG = 20;
const int N = 5e5 + 5;

int dep[N];
int closest[N];
int pr[LOG][N];
bool covered[N];
vector<int> g[N];

void bfs(vector<int>& sheeps) {
  memset(closest, -1, sizeof closest);
  queue<int> que; 
  for (int sheep : sheeps) {
    que.push(sheep);
    closest[sheep] = 0; 
  }
  while (!que.empty()) {
    int v = que.front();
    que.pop();
    for (int u : g[v]) {
      if (closest[u] == -1) {
        closest[u] = closest[v] + 1; 
        que.push(u); 
      }
    }
  }
}

void dfs(int v, int p) {
  for (int u : g[v]) {
    if (u == p) continue; 
    dep[u] = dep[v] + 1; 
    pr[0][u] = v;
    for (int j = 1; j < LOG; ++j) {
      pr[j][u] = pr[j - 1][pr[j - 1][u]];
    }
    dfs(u, v);
  }
}

void dfs2(int v, int p) {
  if (covered[v]) return;
  covered[v] = true; 
  for (int u : g[v]) {
    if (u == p) continue; 
    if (closest[u] == closest[v] - 1) {
      dfs2(u, v); 
    }
  }
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int n, k;
  cin >> n >> k;
  for(int i = 0; i < n - 1; ++i) {
    int u, v;
    cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  vector<int> sheeps(k);
  for (int i = 0; i < k; ++i) {
    cin >> sheeps[i];
  }
  dfs(1, 0);
  bfs(sheeps);
  sort(sheeps.begin(), sheeps.end(), [&](int u, int v) {
    return dep[u] < dep[v];
  });
  vector<int> shepherds;
  for (int i = k - 1; i >= 0; --i) {
    int sheep = sheeps[i];
    if (covered[sheep]) continue; 
    int up = 0;
    int newShephered = sheep;
    for (int j = LOG - 1; j >= 0; --j) {
      if (closest[pr[j][newShephered]] == up + (1 << j)) {
        newShephered = pr[j][newShephered];
        up += 1 << j;
      }
    }
    dfs2(newShephered, newShephered);
    shepherds.push_back(newShephered);
  }
  cout << shepherds.size() << '\n';
  for (int shepherd : shepherds) {
    cout << shepherd << ' ';
  }
  return 0;
}

• Subtask 1: 8 / 8
• Subtask 2: 18 / 18
• Subtask 3: 23 / 23
• Subtask 4: 51 / 51