49 lines
1.3 KiB
C++
49 lines
1.3 KiB
C++
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// WARN: Input could contain multiple edges, but not self loops
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//
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// Returns: (BCC count, indices of BCCs of each vertex)
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//
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// BCC index starts from 1
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pair<int, vector<vector<int>>> vbcc(const vector<vector<int>>& ch) {
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int n = ch.size() - 1;
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vector<vector<int>> c(n + 1); // a vertex could be contained in multiple vBCCs
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int tm = 0;
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int cnt = 0;
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vector<int> low(n + 1), dfn(n + 1);
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vector<int> stack;
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auto dfs = [&] (auto dfs, int v, int pa) -> void {
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int son = 0;
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low[v] = dfn[v] = ++tm;
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stack.emplace_back(v);
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for (auto&& u : ch[v]) {
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if (u == pa) continue;
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son += 1;
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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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if (low[u] >= dfn[v]) {
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cnt += 1;
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int z;
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do {
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z = popback(stack);
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c[z].emplace_back(cnt);
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} while (z != u);
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c[v].emplace_back(cnt);
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}
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}
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chmin(low[v], dfn[u]);
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}
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if (pa == 0 and son == 0) {
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cnt += 1;
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c[v].emplace_back(cnt);
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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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