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Add graph/vbcc.cc 

Signed-off-by: subcrip <contact@subc.rip>
This commit is contained in:
subcrip 2024-11-28 08:36:38 +00:00
parent 469333e1ca
commit 129bce7a32
1 changed files with 48 additions and 0 deletions
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graph/vbcc.cc Normal file
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// WARN: Input could contain multiple edges, but not self loops
//
// Returns: (BCC count, indices of BCCs of each vertex)
//
// BCC index starts from 1
pair<int, vector<vector<int>>> vbcc(const vector<vector<int>>& ch) {
int n = ch.size() - 1;
vector<vector<int>> c(n + 1); // a vertex could be contained in multiple vBCCs
int tm = 0;
int cnt = 0;
vector<int> low(n + 1), dfn(n + 1);
vector<int> stack;
auto dfs = [&] (auto dfs, int v, int pa) -> void {
int son = 0;
low[v] = dfn[v] = ++tm;
stack.emplace_back(v);
for (auto&& u : ch[v]) {
if (u == pa) continue;
son += 1;
if (not dfn[u]) {
dfs(dfs, u, v);
chmin(low[v], low[u]);
if (low[u] >= dfn[v]) {
cnt += 1;
int z;
do {
z = popback(stack);
c[z].emplace_back(cnt);
} while (z != u);
c[v].emplace_back(cnt);
}
}
chmin(low[v], dfn[u]);
}
if (pa == 0 and son == 0) {
cnt += 1;
c[v].emplace_back(cnt);
}
};
for (int i = 1; i <= n; ++i) {
if (not dfn[i]) {
dfs(dfs, i, 0);
}
}
return { cnt, c };
}