Submission #960491

#	Time	Username	Problem	Language	Result	Execution time	Memory
960491		abczz	Mergers (JOI19_mergers)	C++14	100 / 100	1121 ms	203364 KiB

mergers

#include <iostream>
#include <vector>
#include <array>
#define ll long long

using namespace std;

vector <ll> adj[500000];
vector <ll> G[500000];
vector <array<ll, 2>> edge;
ll n, k, a, b, p, cnt, f, A[500000], dp[500000], D[500000], H[500000], P[500000], bl[500000][19], deg[500000];

ll dsu(ll u) {
  if (P[u] == u) return u;
  else return P[u] = dsu(P[u]);
}

void dfs(ll u, ll p) {
  for (auto v : adj[u]) {
    if (v != p) {
      D[v] = D[u]+1;
      dfs(v, u);
      bl[v][0] = u;
    }
  }
}

ll lca(ll a, ll b) {
  if (D[a] > D[b]) swap(a, b);
  ll db = D[b];
  for (int i=18; i>=0; --i) {
    if (db-(1LL<<i) >= D[a]) {
      db -= (1LL<<i);
      b = bl[b][i];
    }
  }
  for (int i=18; i>=0; --i) {
    if (bl[a][i] != bl[b][i]) {
      a = bl[a][i], b = bl[b][i];
    }
  }
  if (a == b) return a;
  else return bl[a][0];
}

void solve(ll u, ll p) {
  dp[u] = H[A[u]];
  for (auto v : adj[u]) {
    if (v != p) {
      solve(v, u);
      if (dp[v] > D[u]) {
        ++cnt;
        edge.push_back({u, v});
      }
      else P[v] = u;
      dp[u] = min(dp[u], dp[v]);
    }
  }
}

int main() {
  cin >> n >> k;
  for (int i=0; i<n-1; ++i) {
    cin >> a >> b;
    --a, --b;
    adj[a].push_back(b);
    adj[b].push_back(a);
  }
  for (int i=0; i<n; ++i) {
    P[i] = i;
    cin >> A[i];
    --A[i];
    G[A[i]].push_back(i);
  }
  dfs(0, -1);
  for (int j=1; j<19; ++j) {
    for (int i=0; i<n; ++i) {
      bl[i][j] = bl[bl[i][j-1]][j-1];
    }
  }
  for (int i=0; i<k; ++i) {
    p = G[i][0];
    for (int j=1; j<G[i].size(); ++j) {
      p = lca(p, G[i][j]);
    }
    H[i] = D[p];
  }
  solve(0, -1);
  for (auto [u, v] : edge) {
    auto a = dsu(u);
    auto b = dsu(v);
    ++deg[a];
    ++deg[b];
  }
  for (int i=0; i<n; ++i) {
    if (deg[i] == 1) ++f;
  }
  cout << (f+1)/2 << '\n';
}

Compilation message (stderr)

mergers.cpp: In function 'int main()':
mergers.cpp:83:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   83 |     for (int j=1; j<G[i].size(); ++j) {
      |                   ~^~~~~~~~~~~~
mergers.cpp:89:13: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   89 |   for (auto [u, v] : edge) {
      |             ^

• Subtask 1: 10 / 10
• Subtask 2: 24 / 24
• Subtask 3: 14 / 14
• Subtask 4: 22 / 22
• Subtask 5: 30 / 30