test/verify/yosupo-two-edge-connected-components-2.test.cpp

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• Last update: 2026-08-10 14:43:01+00:00
• Problem: https://judge.yosupo.jp/problem/two_edge_connected_components

Depends on

• Incremental Bridge Connectivity (graph/connected-components/incremental-bridge-connectivity.hpp)
• Union Find (structure/union-find/union-find.hpp)

Code

// clang-format off
// competitive-verifier: PROBLEM https://judge.yosupo.jp/problem/two_edge_connected_components
// clang-format on

#include <algorithm>
#include <cstddef>
#include <cstdio>
#include <iostream>
#include <string>
#include <utility>
#include <vector>

#include "../../graph/connected-components/incremental-bridge-connectivity.hpp"

using namespace std;

int main() {
  int n, m;
  cin >> n >> m;
  IncrementalBridgeConnectivity ibc(n);
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    ibc.add_edge(a, b);
  }
  vector<int> id(n, -1);
  int k = 0;
  vector<vector<int> > ans(n);
  for (int i = 0; i < n; i++) {
    int r = ibc.find(i);
    if (id[r] == -1) {
      id[r] = k;
      k += 1;
    }
    ans[id[r]].push_back(i);
  }
  cout << k << "\n";
  for (int i = 0; i < k; i++) {
    cout << ans[i].size();
    for (int v : ans[i]) cout << " " << v;
    cout << "\n";
  }
}

#line 1 "test/verify/yosupo-two-edge-connected-components-2.test.cpp"
// clang-format off
// competitive-verifier: PROBLEM https://judge.yosupo.jp/problem/two_edge_connected_components
// clang-format on

#include <algorithm>
#include <cstddef>
#include <cstdio>
#include <iostream>
#include <string>
#include <utility>
#include <vector>

#line 2 "graph/connected-components/incremental-bridge-connectivity.hpp"

#line 4 "graph/connected-components/incremental-bridge-connectivity.hpp"
#include <unordered_set>
#line 7 "graph/connected-components/incremental-bridge-connectivity.hpp"

#line 2 "structure/union-find/union-find.hpp"

#line 7 "structure/union-find/union-find.hpp"

struct UnionFind {
  std::vector<int> data;

  UnionFind() = default;

  explicit UnionFind(std::size_t sz) : data(sz, -1) {}

  bool unite(int x, int y) {
    x = find(x), y = find(y);
    if (x == y) return false;
    if (data[x] > data[y]) std::swap(x, y);
    data[x] += data[y];
    data[y] = x;
    return true;
  }

  int find(int k) {
    if (data[k] < 0) return (k);
    return data[k] = find(data[k]);
  }

  int size(int k) { return -data[find(k)]; }

  bool same(int x, int y) { return find(x) == find(y); }

  std::vector<std::vector<int>> groups() {
    int n = (int)data.size();
    std::vector<std::vector<int>> ret(n);
    for (int i = 0; i < n; i++) {
      ret[find(i)].emplace_back(i);
    }
    ret.erase(
        std::remove_if(ret.begin(), ret.end(),
                       [&](const std::vector<int>& v) { return v.empty(); }),
        ret.end());
    return ret;
  }
};
#line 9 "graph/connected-components/incremental-bridge-connectivity.hpp"

struct IncrementalBridgeConnectivity {
 private:
  UnionFind cc, bcc;
  std::vector<int> bbf;
  std::size_t bridge;

  int size() { return bbf.size(); }

  int par(int x) { return bbf[x] == size() ? size() : bcc.find(bbf[x]); }

  int lca(int x, int y) {
    std::unordered_set<int> used;
    for (;;) {
      if (x != size()) {
        if (!used.insert(x).second) return x;
        x = par(x);
      }
      std::swap(x, y);
    }
  }

  void compress(int x, int y) {
    while (bcc.find(x) != bcc.find(y)) {
      int nxt = par(x);
      bbf[x] = bbf[y];
      bcc.unite(x, y);
      x = nxt;
      --bridge;
    }
  }

  void link(int x, int y) {
    int v = x, pre = y;
    while (v != size()) {
      int nxt = par(v);
      bbf[v] = pre;
      pre = v;
      v = nxt;
    }
  }

 public:
  IncrementalBridgeConnectivity() = default;

  explicit IncrementalBridgeConnectivity(int sz)
      : cc(sz), bcc(sz), bbf(sz, sz), bridge(0) {}

  int find(int k) { return bcc.find(k); }

  std::size_t bridge_size() const { return bridge; }

  void add_edge(int x, int y) {
    x = bcc.find(x);
    y = bcc.find(y);
    if (cc.find(x) == cc.find(y)) {
      int w = lca(x, y);
      compress(x, w);
      compress(y, w);
    } else {
      if (cc.size(x) > cc.size(y)) std::swap(x, y);
      link(x, y);
      cc.unite(x, y);
      ++bridge;
    }
  }
};
#line 14 "test/verify/yosupo-two-edge-connected-components-2.test.cpp"

using namespace std;

int main() {
  int n, m;
  cin >> n >> m;
  IncrementalBridgeConnectivity ibc(n);
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    ibc.add_edge(a, b);
  }
  vector<int> id(n, -1);
  int k = 0;
  vector<vector<int> > ans(n);
  for (int i = 0; i < n; i++) {
    int r = ibc.find(i);
    if (id[r] == -1) {
      id[r] = k;
      k += 1;
    }
    ans[id[r]].push_back(i);
  }
  cout << k << "\n";
  for (int i = 0; i < k; i++) {
    cout << ans[i].size();
    for (int v : ans[i]) cout << " " << v;
    cout << "\n";
  }
}

Test cases

Env	Name	Status	Elapsed	Memory
g++	example_00	AC	2 ms	4 MB
g++	example_01	AC	2 ms	4 MB
g++	example_02	AC	2 ms	3 MB
g++	large_cycle_00	AC	70 ms	10 MB
g++	max_random_00	AC	123 ms	15 MB
g++	max_random_01	AC	124 ms	15 MB
g++	max_random_02	AC	123 ms	15 MB
g++	random_1_00	AC	91 ms	10 MB
g++	random_1_01	AC	97 ms	12 MB
g++	random_1_02	AC	63 ms	6 MB
g++	random_2_00	AC	37 ms	4 MB
g++	random_2_01	AC	10 ms	4 MB
g++	random_2_02	AC	52 ms	5 MB
g++	random_2_03	AC	72 ms	5 MB
g++	random_2_04	AC	29 ms	4 MB
g++	small_random_1_00	AC	2 ms	3 MB
g++	small_random_1_01	AC	2 ms	3 MB
g++	small_random_1_02	AC	2 ms	4 MB
g++	small_random_2_00	AC	2 ms	4 MB
g++	small_random_2_01	AC	2 ms	3 MB
g++	small_random_2_02	AC	2 ms	4 MB
clang++	example_00	AC	2 ms	4 MB
clang++	example_01	AC	2 ms	4 MB
clang++	example_02	AC	2 ms	4 MB
clang++	large_cycle_00	AC	77 ms	10 MB
clang++	max_random_00	AC	127 ms	15 MB
clang++	max_random_01	AC	127 ms	15 MB
clang++	max_random_02	AC	126 ms	15 MB
clang++	random_1_00	AC	90 ms	10 MB
clang++	random_1_01	AC	94 ms	12 MB
clang++	random_1_02	AC	63 ms	6 MB
clang++	random_2_00	AC	36 ms	4 MB
clang++	random_2_01	AC	10 ms	4 MB
clang++	random_2_02	AC	53 ms	5 MB
clang++	random_2_03	AC	74 ms	5 MB
clang++	random_2_04	AC	30 ms	4 MB
clang++	small_random_1_00	AC	2 ms	4 MB
clang++	small_random_1_01	AC	2 ms	4 MB
clang++	small_random_1_02	AC	2 ms	4 MB
clang++	small_random_2_00	AC	2 ms	4 MB
clang++	small_random_2_01	AC	2 ms	4 MB
clang++	small_random_2_02	AC	2 ms	4 MB

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