80 lines
1.6 KiB
C++
80 lines
1.6 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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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(Digraph<T> G) : G(G) {}
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std::vector<SCC<T>> execute();
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void strongConnect(const T& v);
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private:
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// Necessary info about vertices when running Tarjan's algorithm
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struct Payload {
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std::int16_t index = -1;
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std::int16_t lowlink = -1;
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bool onStack = false;
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};
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Digraph<T> G;
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std::stack<T> S;
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std::int16_t index = 0;
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std::map<T, Payload> p;
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std::vector<SCC<T>> SCCs;
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};
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template<typename T>
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void Tarjan<T>::strongConnect(const T& v) {
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p[v].index = p[v].lowlink = index++;
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p[v].onStack = true;
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S.push(v);
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for (const auto& w : G.adjMatrix[v]) {
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if (p[w].index == -1) {
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strongConnect(w);
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p[v].lowlink = std::min(p[v].lowlink, p[w].lowlink);
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} else if (p[w].onStack) {
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p[v].lowlink = std::min(p[v].lowlink, p[w].index);
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}
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}
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// If v is a root node, pop the stack and generate an SCC
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if (p[v].lowlink == p[v].index) {
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//std::vector<T> scc;
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std::map<T, std::set<T>> scc;
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bool finished = false;
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do {
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const auto w = S.top();
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S.pop();
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p[w].onStack = false;
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scc[w] = G.adjMatrix[w];
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finished = p[w].index == p[v].index;
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} while (!finished);
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SCCs.push_back(scc);
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}
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}
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template<typename T>
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std::vector<SCC<T>> Tarjan<T>::execute() {
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for (const auto& v : G.vertices) {
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if (p[v].index == -1) {
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strongConnect(v);
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}
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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 |