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vector<vector<edge>> adjlist;
vector<int> num;
int counter, rootCount, root;
vector<bool> isArt;
vector<edge> bridges, st;
vector<vector<edge>> bcc;
int dfs(int v, int parent = -1) {
int me = num[v] = ++counter, top = me;
for (edge& e : adjlist[v]) {
if (e.id == parent){}
else if (num[e.to]) {
top = min(top, num[e.to]);
if (num[e.to] < me) st.push_back(e);
} else {
if (v == root) rootCount++;
int si = sz(st);
int up = dfs(e.to, e.id);
top = min(top, up);
if (up >= me) isArt[v] = true;
if (up > me) bridges.push_back(e);
if (up <= me) st.push_back(e);
if (up == me) {
bcc.emplace_back();
while (sz(st) > si) {
bcc.back().push_back(st.back());
st.pop_back();
}}}}
return top;
}
void findArticulationPoints() {
counter = 0;
num.assign(sz(adjlist), 0);
isArt.assign(sz(adjlist), false);
bridges.clear();
st.clear();
bcc.clear();
for (int v = 0; v < sz(adjlist); v++) {
if (!num[v]) {
root = v;
rootCount = 0;
dfs(v);
isArt[v] = rootCount > 1;
}}}
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