Submission #35971

#	Time	Username	Problem	Language	Result	Execution time	Memory
35971		funcsr	Pipes (CEOI15_pipes)	C++14	100 / 100	4967 ms	14184 KiB

pipes

#include <iostream>
#include <fstream>
#include <bitset>
#include <cassert>
#include <vector>
#define rep(i, n) for (int i=0; i<(n); i++)
#define pb push_back

using namespace std;
struct UnionFind {
  int U[100000];
  UnionFind(int N) {
    rep(i, N) U[i] = i;
  }
  int find(int x) {
    if (U[x] == x) return x;
    return U[x] = find(U[x]);
  }
  void unite(int x, int y) {
    x = find(x), y = find(y);
    if (x == y) return;
    U[x] = y;
  }
  bool same(int x, int y) {
    return find(x) == find(y);
  }
};

int N, M;
vector<int> G[100000];

int R[100000];
int U[17][100000];
void dfs(int x, int p, int r) {
  R[x] = r;
  U[0][x] = p;
  for (int t : G[x]) {
    if (t == p) continue;
    dfs(t, x, r+1);
  }
}

int T[100000];
int lca(int x, int y) {
  if (R[x] < R[y]) swap(x, y);
  for (int b=16; b>=0; b--) if ((R[x]-R[y])>>b) x = U[b][x];
  if (x == y) return x;
  for (int b=16; b>=0; b--) if (U[b][x] != U[b][y]) x = U[b][x], y = U[b][y];
  return U[0][x];
}
bool used[100000];
void dfs2(int x, int p) {
  used[x] = true;
  for (int t : G[x]) {
    if (t == p) continue;
    dfs2(t, x);
    T[x] += T[t];
  }
  if (p != -1 && T[x] == 0) cout << x+1 << " " << p+1 << "\n";
}


signed main() {
  ifstream cin("/dev/stdin");
  cin >> N >> M;
  auto uf = new UnionFind(N);
  auto backward = new bitset<6000000>();
  rep(i, M) {
    int u, v;
    cin >> u >> v;
    u--, v--;
    if (uf->same(u, v)) {
      backward->set(i);
    }
    else {
      uf->unite(u, v);
      G[u].pb(v);
      G[v].pb(u);
    }
  }
  delete uf;
  rep(i, N) R[i] = -1;
  rep(i, N) if (R[i] == -1) dfs(i, -1, 0);
  rep(k, 16) rep(i, N) {
    if (U[k][i] == -1) U[k+1][i] = -1;
    U[k+1][i] = U[k][U[k][i]];
  }

  cin.seekg(0);
  int nn, nm;
  cin >> nn >> nm;
  assert(N == nn && M == nm);
  rep(i, M) {
    int u, v;
    u = 0, v = 0;
    cin >> u >> v;
    u--, v--;
    if (backward->test(i)) {
      if (R[u] > R[v]) swap(u, v);
      T[u]++;
      T[v]++;
      T[lca(u, v)]-=2;
    }
  }
  delete backward;
  rep(i, N) if (!used[i]) dfs2(i, -1);
  return 0;
}

• Subtask 1: 10 / 10
• Subtask 2: 10 / 10
• Subtask 3: 10 / 10
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 10 / 10
• Subtask 9: 10 / 10
• Subtask 10: 10 / 10