Submission #577218

#	Time	Username	Problem	Language	Result	Execution time	Memory
577218		Sam_a17	Cat in a tree (BOI17_catinatree)	C++14	100 / 100	500 ms	43588 KiB

catinatree

#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
//#include "temp.cpp"
#include <cstdio>
using namespace std;

#ifndef ONLINE_JUDGE
#define dbg(x) cerr << #x <<" "; print(x); cerr << endl;
#else
#define dbg(x)
#endif

#define sz(x) (int((x).size()))
#define len(x) (int)x.length()
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define clr(x) (x).clear()
#define uniq(x) x.resize(unique(all(x)) - x.begin());
#define blt __builtin_popcount

#define pb push_back
#define popf pop_front
#define popb pop_back

void print(long long t) {cerr << t;}
void print(int t) {cerr << t;}
void print(string t) {cerr << t;}
void print(char t) {cerr << t;}
void print(double t) {cerr << t;}
void print(long double t) {cerr << t;}
void print(unsigned long long t) {cerr << t;}

template <class T, class V> void print(pair <T, V> p);
template <class T> void print(vector <T> v);
template <class T> void print(set <T> v);
template <class T, class V> void print(map <T, V> v);
template <class T> void print(multiset <T> v);
template <class T, class V> void print(T v[],V n) {cerr << "["; for(int i = 0; i < n; i++) {print(v[i]); cerr << " "; } cerr << "]";}
template <class T, class V> void print(pair <T, V> p) {cerr << "{"; print(p.first); cerr << ","; print(p.second); cerr << "}";}
template <class T> void print(vector <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(set <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T> void print(multiset <T> v) {cerr << "[ "; for (T i : v) {print(i); cerr << " ";} cerr << "]";}
template <class T, class V> void print(map <T, V> v) {cerr << "[ "; for (auto i : v) {print(i); cerr << " ";} cerr << "]";}

#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
#define nl '\n'

// for grid problems
int dx[8] = {-1,0,1,0,1,-1,1,-1};
int dy[8] = {0,1,0,-1,1,1,-1,-1};

// lowest / (1 << 17) >= 1e5 / (1 << 18) >= 2e5 / (1 << 21) >= 1e6
void fastIO() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr); cout.tie(nullptr);
}
// file in/out
void setIO(string str = "") {
  fastIO();

  if (str != "") {
    freopen((str + ".in").c_str(), "r", stdin);
    freopen((str + ".out").c_str(), "w", stdout);
  }
}
// Indexed Set
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
const int N = 2e5 + 10, LOG = 22;
int n, m, sz[N], compSize, p[N], best[N], up[N][LOG], depth[N];
vector<int> adj[N];
bool used[N];

void dfs_lca(int node, int parent) {
  for(auto i: adj[node]) {
    if(i == parent) continue;
    up[i][0] = node;
    for(int j = 1; j < LOG; j++) {
      up[i][j] = up[up[i][j - 1]][j - 1];
    }
    depth[i] = depth[node] + 1;
    dfs_lca(i, node);
  }
}

int lca(int a, int b) {
  if(a == b) {
    return a;
  }

  if(depth[a] < depth[b]) {
    swap(a, b);
  }

  int delta = depth[a] - depth[b];

  for(int i = 0; i < LOG; i++) {
    if(delta & (1 << i)) {
      a = up[a][i];
    }
  }

  if(a == b) {
    return a;
  }

  for(int i = LOG - 1; i >= 0; i--) {
    if(up[a][i] != up[b][i]) {
      a = up[a][i], b = up[b][i];
    }
  }

  return up[a][0];
}

int dist(int a, int b) {
  return depth[a] + depth[b] - 2 * depth[lca(a, b)];
}

int dfs_sz(int node, int parent) {
  sz[node] = 1, compSize++;
  for(auto i: adj[node]) {
    if(i == parent || used[i]) continue;
    sz[node] += dfs_sz(i, node);
  }
  return sz[node];
}

int get_centroid(int node, int parent) {
  for(auto i: adj[node]) {
    if(i == parent || used[i]) continue;
    if(2 * sz[i] > compSize) {
      return get_centroid(i, node);
    }
  }
  return node;
}

int find_centroid(int node, int parent) {
  compSize = 0;
  dfs_sz(node, 0);
  int centroid = get_centroid(node, 0);
  return centroid;
}

void centroid_decomposition() {
  queue<pair<int, int>> q;
  q.push({1, 0});
  dfs_lca(1, 0);

  while(!q.empty()) {
    auto u = q.front();
    q.pop();

    int centroid = find_centroid(u.first, 0);

    if(u.second) {
      p[centroid] = u.second;
    }

    used[centroid] = true;
    for(auto i: adj[centroid]) {
      if(used[i]) continue;
      q.push({i, centroid});
    }

  }
}

void init() {
  for(int i = 1; i <= n; i++) {
    best[i] = 1e8;
  }
}

void update(int node) {
  int curr = node;
  while(curr) {
    best[curr] = min(best[curr], dist(curr, node));
    curr = p[curr];
  }
}

int query(int node) {
  int curr = node, answ = best[curr];
  while(curr) {
    answ = min(answ, dist(curr, node) + best[curr]);
    curr = p[curr];
  }
  return answ;
}

void solve_() {
  cin >> n >> m;
  for(int i = 2; i <= n; i++) {
    int a; cin >> a, a++;
    adj[a].push_back(i);
    adj[i].push_back(a);
  }

  centroid_decomposition();
  
  //
  init();
  
  vector<pair<int, int>> order;

  for(int i = 1; i <= n; i++) {
    order.push_back({depth[i], i});
  }

  sort(rall(order));

  int answ = 0;
  for(int i = 1; i <= n; i++) {
    int distance = query(order[i - 1].second);
    if(distance < m) continue;
    update(order[i - 1].second);
    answ++;
  }

  printf("%d\n", answ);
}

int main() {
  setIO("");

  auto solve = [&](int test_case)-> void {
    while(test_case--) {
      solve_();
    }
  };

  int test_cases = 1;
  solve(test_cases);

  return 0;
}

Compilation message (stderr)

catinatree.cpp: In function 'void setIO(std::string)':
catinatree.cpp:63:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   63 |     freopen((str + ".in").c_str(), "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
catinatree.cpp:64:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   64 |     freopen((str + ".out").c_str(), "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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