Submission #1174394

#	Time	Username	Problem	Language	Result	Execution time	Memory
1174394		_ncng.nyr	Cat in a tree (BOI17_catinatree)	C++20	0 / 100	1008 ms	5256 KiB

catinatree

#include<bits/stdc++.h>

using namespace std;

const int N = 2e5 + 5;

int n, D, it;
int in[N], out[N], h[N];
int up[20][N];
vector<int> ad[N];

void dfs(int u, int p) {
  in[u] = ++it;
  if(u == 1) for(int i = 0; i <= 18; ++i) up[i][u] = u;
  else for(int i = 1; i <= 18; ++i) up[i][u] = up[i - 1][up[i - 1][u]];

  for(auto v : ad[u]) {
    if(v == p) continue;
    up[0][v] = u;
    h[v] = h[u] + 1;
    dfs(v, u);
  }
  out[u] = it;
}

int anc(int u, int v) {
  return (in[u] <= in[v] && out[v] <= out[u]);
}

int lca(int u, int v) {
  if(anc(u, v)) return u;
  int ret = u;
  for(int i = 18; i >= 0; --i)
    if(anc(up[i][u], v)) ret = up[i][u];
    else u = up[i][u];
  return ret;
}

int dist(int u, int v) {
  return h[u] + h[v] - 2 * h[lca(u, v)];
}

namespace sub1 {
  int ans = 0;
  void solve() {
    for(int mask = 0; mask < (1 << n); ++mask) {
      vector<int> v;
      for(int i = 1; i <= n; ++i)
        if((mask >> i - 1) & 1) v.push_back(i);

      bool ok = 1;
      for(int i = 0; i < v.size(); ++i)
        for(int j = 0; j < v.size(); ++j)
          if(i != j && dist(v[i], v[j]) < D) ok = 0;

      if(ok) ans = max(ans, __builtin_popcount(mask));
    }

    cout << ans;
  }
}

int32_t main() {
  cin.tie(0)->sync_with_stdio(0);

  if(fopen("task.inp", "r")) {
    freopen("task.inp", "r", stdin);
    freopen("task.out", "w", stdout);
  }

  cin >> n >> D;

  for(int i = 2; i <= n; ++i) {
    int u; cin >> u; ++u;
    ad[u].push_back(i);
    ad[i].push_back(u);
  }

  dfs(1, 0);

  if(n <= 18) sub1 :: solve();
}

Compilation message (stderr)

catinatree.cpp: In function 'int32_t main()':
catinatree.cpp:67:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   67 |     freopen("task.inp", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
catinatree.cpp:68:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   68 |     freopen("task.out", "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 11
• Subtask 2: 0 / 40
• Subtask 3: 0 / 49