11#include < bits/stdc++.h>
22using namespace std ;
3- #define pii pair<int ,int >
43
54struct BlockCutTree {
65 vector<vector<int >> g, tree, comp;
@@ -17,34 +16,21 @@ struct BlockCutTree {
1716 for (int u=0 ; u<n; u++, chd=0 ) if (pre[u] == -1 ) // if graph is disconected
1817 tarjan (u, -1 ), makeComp (-1 ); // find cut vertex and make components
1918
20- for (int i=0 , ct=1 ; i<comp.size (); i++, ct=1 ){ // remove components with only cuts
21- for (auto u : comp[i]) ct &= cut[u];
22- if (ct) swap (comp[i], comp.back ()), comp.pop_back (), i--;
23- }
24- 2519 for (int u=0 ; u<n; u++) if (cut[u]) comp.emplace_back (1 , u); // create cut components
20+ for (int i=0 ; i<comp.size (); i++) // mark id of each node
21+ for (auto u : comp[i]) id[u] = i;
2622
27- for (int i=0 ; i<comp.size (); i++) // mark id of each node
28- for (auto u : comp[i])
29- id[u] = i;
30- 31- tree.resize (comp.size ()); // creates tree (looking only edges from cut points)
32- pre.assign (comp.size (), 1 );
33- 34- for (int u=0 ; u<n; u++) if (cut[u]){
35- for (auto v : g[u]) if (pre[id[v]] && (!cut[v] || u<v)) addt (id[u], id[v]), pre[id[v]]=0 ;
36- for (auto v : g[u]) pre[id[v]] = 1 ;
37- }
23+ tree.resize (comp.size ());
24+ for (int i=0 ; i<comp.size (); i++)
25+ for (auto u : comp[i]) if (id[u] != i)
26+ tree[i].push_back (id[u]),
27+ tree[id[u]].push_back (i);
3828 }
3929private:
4030 vector<int > pre, low;
41- vector<pii > st;
31+ vector<pair< int , int > > st;
4232 int n, clk = 0 , chd=0 , ct, a, b;
43- void addt (int u, int v){
44- tree[u].push_back (v);
45- tree[v].push_back (u);
46- }
47- 33+ 4834 void makeComp (int u){
4935 comp.emplace_back ();
5036 do {
@@ -71,13 +57,14 @@ struct BlockCutTree {
7157 }
7258};
7359
60+ 7461/* LATEX_DESC_BEGIN***************************
7562Block Cut Tree - BiConnected Component
7663BlockCutTree bcc(n);
7764bcc.addEdge(u, v);
7865bcc.build();
7966
80- bcc.tree -> graph of BlockCutTree
67+ bcc.tree -> graph of BlockCutTree (tree.size() <= 2n)
8168bcc.id[u] -> componet of u in the tree
8269bcc.cut[u] -> 1 if u is a cut vertex; 0 otherwise
8370bcc.comp[i] -> vertex of comp i (cut are part of multiple comp)
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