graph/twoedgeconnectedcomponents.cpp

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• Last update: 2020-10-27 16:01:15+09:00

Verified with

• test/aoj/0377.test.cpp
• test/aoj/0415.test.cpp
• test/yosupo/two_edge_connected_components.test.cpp

Code

#ifndef call_from_test
#include <bits/stdc++.h>
using namespace std;
#endif
//BEGIN CUT HERE
// work with multigraph
struct TwoEdgeConnectedComponents{
  vector<int> ord,low,par,blg,sz;
  vector<vector<int>> G,C;

  TwoEdgeConnectedComponents(int n):
    ord(n,-1),low(n),par(n,-1),blg(n,-1),sz(n,1),G(n){}

  void add_edge(int u,int v){
    if(u==v) return;
    G[u].emplace_back(v);
    G[v].emplace_back(u);
  }

  bool is_bridge(int u,int v){
    if(ord[u]>ord[v]) swap(u,v);
    return ord[u]<low[v];
  }

  void dfs(int v,int &pos){
    ord[v]=low[v]=pos++;
    int dup=0;
    for(int u:G[v]){
      if(u==par[v] and !dup){
        dup=1;
        continue;
      }
      if(~ord[u]){
        low[v]=min(low[v],ord[u]);
        continue;
      }
      par[u]=v;
      dfs(u,pos);
      sz[v]+=sz[u];
      low[v]=min(low[v],low[u]);
    }
  }

  void fill_component(int v){
    C[blg[v]].emplace_back(v);
    for(int u:G[v]){
      if(~blg[u] or is_bridge(u,v)) continue;
      blg[u]=blg[v];
      fill_component(u);
    }
  }

  void add_component(int v,int &k){
    if(~blg[v]) return;
    blg[v]=k++;
    C.emplace_back();
    fill_component(v);
  }

  int build(){
    int n=G.size(),pos=0;
    for(int i=0;i<n;i++)
      if(ord[i]<0) dfs(i,pos);

    int k=0;
    for(int i=0;i<n;i++) add_component(i,k);

    return k;
  }

  const vector<int>& operator[](int i)const{return C[i];}

  vector<vector<int>> forest(){
    int n=G.size(),k=C.size();
    vector<vector<int>> T(k);
    for(int v=0;v<n;v++)
      for(int u:G[v])
        if(blg[v]!=blg[u])
          T[blg[v]].emplace_back(blg[u]);
    return T;
  }
};
//END CUT HERE
#ifndef call_from_test
//INSERT ABOVE HERE
signed main(){
  return 0;
}
#endif

#line 1 "graph/twoedgeconnectedcomponents.cpp"

#include <bits/stdc++.h>
using namespace std;
#endif
//BEGIN CUT HERE
// work with multigraph
struct TwoEdgeConnectedComponents{
  vector<int> ord,low,par,blg,sz;
  vector<vector<int>> G,C;

  TwoEdgeConnectedComponents(int n):
    ord(n,-1),low(n),par(n,-1),blg(n,-1),sz(n,1),G(n){}

  void add_edge(int u,int v){
    if(u==v) return;
    G[u].emplace_back(v);
    G[v].emplace_back(u);
  }

  bool is_bridge(int u,int v){
    if(ord[u]>ord[v]) swap(u,v);
    return ord[u]<low[v];
  }

  void dfs(int v,int &pos){
    ord[v]=low[v]=pos++;
    int dup=0;
    for(int u:G[v]){
      if(u==par[v] and !dup){
        dup=1;
        continue;
      }
      if(~ord[u]){
        low[v]=min(low[v],ord[u]);
        continue;
      }
      par[u]=v;
      dfs(u,pos);
      sz[v]+=sz[u];
      low[v]=min(low[v],low[u]);
    }
  }

  void fill_component(int v){
    C[blg[v]].emplace_back(v);
    for(int u:G[v]){
      if(~blg[u] or is_bridge(u,v)) continue;
      blg[u]=blg[v];
      fill_component(u);
    }
  }

  void add_component(int v,int &k){
    if(~blg[v]) return;
    blg[v]=k++;
    C.emplace_back();
    fill_component(v);
  }

  int build(){
    int n=G.size(),pos=0;
    for(int i=0;i<n;i++)
      if(ord[i]<0) dfs(i,pos);

    int k=0;
    for(int i=0;i<n;i++) add_component(i,k);

    return k;
  }

  const vector<int>& operator[](int i)const{return C[i];}

  vector<vector<int>> forest(){
    int n=G.size(),k=C.size();
    vector<vector<int>> T(k);
    for(int v=0;v<n;v++)
      for(int u:G[v])
        if(blg[v]!=blg[u])
          T[blg[v]].emplace_back(blg[u]);
    return T;
  }
};
//END CUT HERE
#ifndef call_from_test
//INSERT ABOVE HERE
signed main(){
  return 0;
}
#endif

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