99 lines
2.4 KiB
C++
99 lines
2.4 KiB
C++
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// WARN: Input should be a simple graph
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//
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// Returns: (BCC count, indices of BCC of each vertex)
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//
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// BCC index starts from 1
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pair<int, vector<int>> ebcc(const vector<vector<int>>& ch) {
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int n = ch.size() - 1;
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vector<int> c(n + 1);
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vector<int> low(n + 1), dfn(n + 1);
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vector<bool> vis(n + 1);
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vector<int> stack;
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int time = 0;
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int cnt = 0;
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auto dfs = [&] (auto dfs, int v, int pa) -> void {
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low[v] = dfn[v] = ++time;
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stack.emplace_back(v);
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vis[v] = 1;
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for (auto&& u : ch[v]) {
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if (u == pa) continue;
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if (not dfn[u]) {
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dfs(dfs, u, v);
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chmin(low[v], low[u]);
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} else if (vis[u]) {
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chmin(low[v], dfn[u]);
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}
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}
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if (dfn[v] == low[v]) {
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cnt += 1;
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c[v] = cnt;
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while (stack.back() != v) {
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c[stack.back()] = cnt;
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vis[stack.back()] = 0;
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stack.pop_back();
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}
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stack.pop_back();
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}
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};
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for (int i = 1; i <= n; ++i) {
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if (not dfn[i]) {
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dfs(dfs, i, 0);
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}
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}
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return { cnt, c };
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}
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// INFO: This function treats vertex pairs that have multiple edges as eBCCs.
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//
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// Returns: (BCC count, indices of BCC of each vertex)
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//
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// BCC index starts from 1
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pair<int, vector<int>> ebcc_with_mult(const vector<vector<pii>>& ch) {
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int n = ch.size() - 1;
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vector<int> c(n + 1);
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vector<int> low(n + 1), dfn(n + 1);
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vector<bool> vis(n + 1);
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vector<int> stack;
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int time = 0;
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int cnt = 0;
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auto dfs = [&] (auto dfs, int v, int prev_idx) -> void {
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low[v] = dfn[v] = ++time;
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stack.emplace_back(v);
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vis[v] = 1;
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for (auto&& [u, i] : ch[v]) {
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if (i == prev_idx) continue;
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if (not dfn[u]) {
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dfs(dfs, u, i);
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chmin(low[v], low[u]);
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} else if (vis[u]) {
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chmin(low[v], dfn[u]);
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}
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}
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if (dfn[v] == low[v]) {
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cnt += 1;
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c[v] = cnt;
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while (stack.back() != v) {
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c[stack.back()] = cnt;
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vis[stack.back()] = 0;
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stack.pop_back();
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}
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stack.pop_back();
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}
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};
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for (int i = 1; i <= n; ++i) {
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if (not dfn[i]) {
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dfs(dfs, i, -1);
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}
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}
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return { cnt, c };
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}
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