Java/DataStructures/Graphs/ConnectedComponent.java at dev · primary-code-test/Java · GitHub

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package DataStructures.Graphs;

import java.util.ArrayList;

import java.util.HashSet;

import java.util.Set;

/**

* A class that counts the number of different connected components in a graph

* @author Lukas Keul, Florian Mercks

class Graph<E extends Comparable<E>> {

class Node {

E name;

public Node(E name) {

this.name = name;

}

class Edge {

Node startNode, endNode;

public Edge(Node startNode, Node endNode) {

this.startNode = startNode;

this.endNode = endNode;

}

ArrayList<Edge> edgeList;

ArrayList<Node> nodeList;

public Graph() {

edgeList = new ArrayList<Edge>();

nodeList = new ArrayList<Node>();

}

/**

* Adds a new Edge to the graph. If the nodes aren't yet in nodeList, they will be added to it.

* @param startNode the starting Node from the edge

* @param endNode the ending Node from the edge

public void addEdge(E startNode, E endNode) {

Node start = null, end = null;

for (Node node : nodeList) {

if (startNode.compareTo(node.name) == 0) {

start = node;

} else if (endNode.compareTo(node.name) == 0) {

end = node;

}

if (start == null) {

start = new Node(startNode);

nodeList.add(start);

}

if (end == null) {

end = new Node(endNode);

nodeList.add(end);

}

edgeList.add(new Edge(start, end));

}

/**

* Main method used for counting the connected components. Iterates through the array of nodes to

* do a depth first search to get all nodes of the graph from the actual node. These nodes are

* added to the array markedNodes and will be ignored if they are chosen in the nodeList.

* @return returns the amount of unconnected graphs

public int countGraphs() {

int count = 0;

Set<Node> markedNodes = new HashSet<Node>();

for (Node n : nodeList) {

if (!markedNodes.contains(n)) {

markedNodes.add(n);

markedNodes.addAll(depthFirstSearch(n, new ArrayList<Node>()));

count++;

}

return count;

}

/**

* Implementation of depth first search.

* @param n the actual visiting node

* @param visited A list of already visited nodes in the depth first search

* @return returns a set of visited nodes

public ArrayList<Node> depthFirstSearch(Node n, ArrayList<Node> visited) {

visited.add(n);

for (Edge e : edgeList) {

if (e.startNode.equals(n) && !visited.contains(e.endNode)) {

depthFirstSearch(e.endNode, visited);

}

return visited;

}

public class ConnectedComponent {

public static void main(String[] args) {

Graph<Character> graphChars = new Graph<>();

// Graph 1

graphChars.addEdge('a', 'b');

graphChars.addEdge('a', 'e');

graphChars.addEdge('b', 'e');

graphChars.addEdge('b', 'c');

graphChars.addEdge('c', 'd');

graphChars.addEdge('d', 'a');

graphChars.addEdge('x', 'y');

graphChars.addEdge('x', 'z');

graphChars.addEdge('w', 'w');

Graph<Integer> graphInts = new Graph<>();

// Graph 2

graphInts.addEdge(1, 2);

graphInts.addEdge(2, 3);

graphInts.addEdge(2, 4);

graphInts.addEdge(3, 5);

graphInts.addEdge(7, 8);

graphInts.addEdge(8, 10);

graphInts.addEdge(10, 8);

System.out.println("Amount of different char-graphs: " + graphChars.countGraphs());

System.out.println("Amount of different int-graphs: " + graphInts.countGraphs());

}

Java/DataStructures/Graphs/ConnectedComponent.java at dev · primary-code-test/Java · GitHub

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