85 lines
1.7 KiB
C++
85 lines
1.7 KiB
C++
#ifndef TARJAN_H_
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#define TARJAN_H_
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#include "graph/scc.h"
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#include <stack>
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#include <vector>
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#include <ranges>
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using namespace graph;
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namespace algo {
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template<typename T>
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class Tarjan {
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public:
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Tarjan() = default;
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Tarjan(std::unordered_map<T, std::unordered_set<T>> adjList) : adjList(adjList) {}
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//
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auto execute();
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//
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void strongConnect(const T& u);
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private:
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std::unordered_map<T, std::unordered_set<T>> adjList;
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std::stack<T> S;
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std::int16_t index = 0;
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std::vector<SCC<T>> SCCs;
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T cid;
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struct Vertex {
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int index = -1;
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int lowlink = -1;
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bool onStack = false;
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};
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std::unordered_map<T, Vertex> vmap;
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};
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template<typename T>
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void Tarjan<T>::strongConnect(const T& u) {
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vmap[u].index = vmap[u].lowlink = index++;
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S.push(u);
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vmap[u].onStack = true;
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for (const auto& w : adjList[u]) {
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if (vmap[w].index == -1) {
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strongConnect(w);
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vmap[u].lowlink = std::min(vmap[u].lowlink, vmap[w].lowlink);
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} else if (vmap[w].onStack) {
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vmap[u].lowlink = std::min(vmap[u].lowlink, vmap[w].index);
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}
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}
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// If u is a root node, pop the stack and generate an SCC
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if (vmap[u].lowlink == vmap[u].index) {
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std::unordered_map<T, std::unordered_set<T>> scc;
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bool finished = false;
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cid = S.top();
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do {
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const auto w = S.top();
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S.pop();
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vmap[w].onStack = false;
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scc[w] = adjList[w];
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finished = (w == u);
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} while (!finished);
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SCCs.push_back({ scc, static_cast<T>(cid) });
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}
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}
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template<typename T>
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auto Tarjan<T>::execute() {
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for (const auto& u : std::views::keys(adjList)) {
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if (vmap[u].index == -1)
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strongConnect(u);
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}
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return SCCs;
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}
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} // namespace algo
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#endif |