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| const int maxn = 100000 + 10;
// == define Edge and Graph ==
class Edge {
public:
int to;
Edge() {}
Edge(int to) : to(to) {}
};
vector<Edge> edges;
vector<int> G[maxn];
// == Edge and Graph finsihed ==
// == tarjan info ==
int n, m;
vector<int> dcc[maxn];
int dfn[maxn], low[maxn], cnt = 0, Clock = 0;
bool cut[maxn];
stack<int> stk;
int root = 0;
void init() {
cnt = 0;
Clock = 0;
root = 0;
edges.clear();
edges.push_back(Edge());
edges.push_back(Edge());
// NIL edges
Set(dfn, 0);
Set(low, 0);
Set(cut, 0);
while(!stk.empty()) stk.pop();
}
// == tarjan info finished ==
// == tarjan main ==
void addEdge(int u, int v) {
edges.push_back(Edge(v));
G[u].push_back(edges.size() - 1);
}
void tarjan(int u) {
dfn[u] = low[u] = ++Clock;
stk.push(u);
if(u == root && G[u].size() == 0) {
// single point
dcc[++cnt].push_back(u);
return;
}
int cld = 0;
_for(i, 0, G[u].size()) {
int eid = G[u][i], v = edges[eid].to;
if(!dfn[v]) {
tarjan(v);
low[u] = min(low[u], low[v]);
// judge cut-point
if(low[v] >= dfn[u]) {
cld++;
if(u != root || cld > 1) cut[u] = true;
// save the point in the same DCC
cnt++;
for(;;) {
int z = stk.top(); stk.pop();
dcc[cnt].push_back(z);
if(z == v) break;
}
dcc[cnt].push_back(u);
}
}
else low[u] = min(low[u], dfn[v]);
}
}
// == tarjan finsihed ==
// == vDCC Graph ==
vector<int> GC[maxn];
vector<Edge> vDCC;
int belong[maxn], newID[maxn];
int num = 0;
void initDCC() {
vDCC.clear();
vDCC.push_back(Edge());
vDCC.push_back(Edge());
// NIL edges
Set(belong, 0);
Set(newID, 0);
num = 0;
}
void add_c(int u, int v) {
vDCC.push_back(Edge(v));
GC[u].push_back(vDCC.size() - 1);
}
// == vDCC finsihed ==
void getDCC() {
// input DCC nodes and data
_rep(i, 1, cnt) {
printf("v-DCC #%d:", i);
_for(j, 0, dcc[i].size()) {
printf(" %d", dcc[i][j]);
}
puts("");
}
// point reduction
num = cnt;
_rep(i, 1, n) if(cut[i]) newID[i] = ++num;
// build new Graph for vDCC
_rep(i, 1, cnt) _for(j, 0, dcc[i].size()) {
int z = dcc[i][j];
if(cut[z]) {
add_c(i, newID[z]), add_c(newID[z], i);
}
else belong[z] = i;
}
// print info
printf("缩点之后的森林，点数 %d, 边数 %d\n", num, (int)(vDCC.size() - 1) >> 1);
printf("下图编号 1～%d 的为原图的v-DCC，编号 >=%d 的为原图的割点\n", cnt, cnt);
for(int i = 2; i < vDCC.size(); i += 2) {
printf("vDCC#%d <-----> vDCC#%d\n", vDCC[i^1].to, vDCC[i].to);
}
}
// == vDCC Graph finished ==
int main() {
freopen("input.txt", "r", stdin);
cin >> n >> m;
init();
_rep(i, 1, m) {
int u, v;
scanf("%d%d", &u, &v);
if(u == v) continue;
addEdge(u, v), addEdge(v, u);
}
// == tarjan ==
_rep(i, 1, n) if(!dfn[i]) {
root = i, tarjan(i);
}
_rep(i, 1, n) if(cut[i]) printf("%d ", i);
puts("are cut vertexes");
// == tarjan finished ==
initDCC();
getDCC();
}
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