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Ingy döt Net 2023-07-01 11:58:00 -04:00
parent 7387c8f97b
commit cb5bb5e222
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Task/Tarjan/Java/tarjan.java Normal file
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import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.Stack;
public final class TarjanSCC {
public static void main(String[] aArgs) {
Graph graph = new Graph(8);
graph.addDirectedEdge(0, 1);
graph.addDirectedEdge(1, 2); graph.addDirectedEdge(1, 7);
graph.addDirectedEdge(2, 3); graph.addDirectedEdge(2, 6);
graph.addDirectedEdge(3, 4);
graph.addDirectedEdge(4, 2); graph.addDirectedEdge(4, 5);
graph.addDirectedEdge(6, 3); graph.addDirectedEdge(6, 5);
graph.addDirectedEdge(7, 0); graph.addDirectedEdge(7, 6);
System.out.println("The strongly connected components are: ");
for ( Set<Integer> component : graph.getSCC() ) {
System.out.println(component);
}
}
}
final class Graph {
public Graph(int aSize) {
adjacencyLists = new ArrayList<Set<Integer>>(aSize);
for ( int i = 0; i < aSize; i++ ) {
vertices.add(i);
adjacencyLists.add( new HashSet<Integer>() );
}
}
public void addDirectedEdge(int aFrom, int aTo) {
adjacencyLists.get(aFrom).add(aTo);
}
public List<Set<Integer>> getSCC() {
for ( int vertex : vertices ) {
if ( ! numbers.keySet().contains(vertex) ) {
stronglyConnect(vertex);
}
}
return stronglyConnectedComponents;
}
private void stronglyConnect(int aVertex) {
numbers.put(aVertex, index);
lowlinks.put(aVertex, index);
index += 1;
stack.push(aVertex);
for ( int adjacent : adjacencyLists.get(aVertex) ) {
if ( ! numbers.keySet().contains(adjacent) ) {
stronglyConnect(adjacent);
lowlinks.put(aVertex, Math.min(lowlinks.get(aVertex), lowlinks.get(adjacent)));
} else if ( stack.contains(adjacent) ) {
lowlinks.put(aVertex, Math.min(lowlinks.get(aVertex), numbers.get(adjacent)));
}
}
if ( lowlinks.get(aVertex) == numbers.get(aVertex) ) {
Set<Integer> stonglyConnectedComponent = new HashSet<Integer>();
int top;
do {
top = stack.pop();
stonglyConnectedComponent.add(top);
} while ( top != aVertex );
stronglyConnectedComponents.add(stonglyConnectedComponent);
}
}
private List<Set<Integer>> adjacencyLists;
private List<Integer> vertices = new ArrayList<Integer>();
private int index = 0;
private Stack<Integer> stack = new Stack<Integer>();
private Map<Integer, Integer> numbers = new HashMap<Integer, Integer>();
private Map<Integer, Integer> lowlinks = new HashMap<Integer, Integer>();
private List<Set<Integer>> stronglyConnectedComponents = new ArrayList<Set<Integer>>();
}