83 lines
1.6 KiB
C++
83 lines
1.6 KiB
C++
#ifndef TARJAN_H_
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#define TARJAN_H_
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#include "graph/graph.h"
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using namespace graph;
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#include <algorithm>
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#include <iostream>
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#include <ranges>
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#include <stack>
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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(Graph<T> G) : G(G) {}
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//
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std::vector<std::vector<T>> run();
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//
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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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Graph<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> vp;
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std::vector<std::vector<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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vp[v].index = vp[v].lowlink = index++;
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vp[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 (vp[w].index == -1) {
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strongConnect(w);
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vp[v].lowlink = std::min(vp[v].lowlink, vp[w].lowlink);
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} else if (vp[w].onStack) {
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vp[v].lowlink = std::min(vp[v].lowlink, vp[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 (vp[v].lowlink == vp[v].index) {
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std::vector<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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vp[w].onStack = false;
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SCC.push_back(w);
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finished = vp[w].index == vp[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<std::vector<T>> Tarjan<T>::run() {
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for (const auto& v : G.vertices) {
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if (vp[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 |