Merge pull request #8222 from pazis/BAEL-3561
BAEL-3561 Prim's Algorithm
This commit is contained in:
Josh Cummings
GitHub
commit
e3f63606e1
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package com.baeldung.algorithms.prim;
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public class Edge {
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private int weight;
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private boolean isIncluded = false;
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private boolean isPrinted = false;
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public Edge(int weight) {
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this.weight = weight;
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}
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public int getWeight() {
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return weight;
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}
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public void setWeight(int weight) {
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this.weight = weight;
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}
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public boolean isIncluded() {
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return isIncluded;
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}
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public void setIncluded(boolean included) {
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isIncluded = included;
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}
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public boolean isPrinted() {
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return isPrinted;
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}
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public void setPrinted(boolean printed) {
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isPrinted = printed;
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}
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}
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package com.baeldung.algorithms.prim;
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import java.util.Iterator;
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import java.util.List;
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import java.util.Map;
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import org.apache.commons.math3.util.Pair;
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public class Prim {
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private List<Vertex> graph;
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public Prim(List<Vertex> graph){
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this.graph = graph;
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}
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public void run(){
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if (graph.size() > 0){
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graph.get(0).setVisited(true);
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}
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while (isDisconnected()){
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Edge nextMinimum = new Edge(Integer.MAX_VALUE);
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Vertex nextVertex = graph.get(0);
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for (Vertex vertex : graph){
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if (vertex.isVisited()){
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Pair<Vertex, Edge> candidate = vertex.nextMinimum();
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if (candidate.getValue().getWeight() < nextMinimum.getWeight()){
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nextMinimum = candidate.getValue();
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nextVertex = candidate.getKey();
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}
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}
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}
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nextMinimum.setIncluded(true);
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nextVertex.setVisited(true);
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}
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}
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private boolean isDisconnected(){
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for (Vertex vertex : graph){
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if (!vertex.isVisited()){
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return true;
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}
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}
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return false;
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}
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public String originalGraphToString(){
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StringBuilder sb = new StringBuilder();
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for (Vertex vertex : graph){
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sb.append(vertex.originalToString());
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}
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return sb.toString();
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}
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public void resetPrintHistory(){
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for (Vertex vertex : graph){
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Iterator<Map.Entry<Vertex,Edge>> it = vertex.getEdges().entrySet().iterator();
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while (it.hasNext()) {
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Map.Entry<Vertex,Edge> pair = it.next();
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pair.getValue().setPrinted(false);
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}
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}
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}
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public String minimumSpanningTreeToString(){
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StringBuilder sb = new StringBuilder();
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for (Vertex vertex : graph){
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sb.append(vertex.includedToString());
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}
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return sb.toString();
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}
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}
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package com.baeldung.algorithms.prim;
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import java.util.HashMap;
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import java.util.Iterator;
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import java.util.Map;
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import org.apache.commons.math3.util.Pair;
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public class Vertex {
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private String label = null;
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private Map<Vertex, Edge> edges = new HashMap<>();
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private boolean isVisited = false;
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public Vertex(String label){
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this.label = label;
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}
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public String getLabel() {
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return label;
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}
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public void setLabel(String label) {
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this.label = label;
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}
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public Map<Vertex, Edge> getEdges() {
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return edges;
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}
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public void addEdge(Vertex vertex, Edge edge){
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if (this.edges.containsKey(vertex)){
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if (edge.getWeight() < this.edges.get(vertex).getWeight()){
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this.edges.replace(vertex, edge);
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}
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} else {
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this.edges.put(vertex, edge);
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}
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}
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public boolean isVisited() {
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return isVisited;
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}
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public void setVisited(boolean visited) {
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isVisited = visited;
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}
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public Pair<Vertex, Edge> nextMinimum(){
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Edge nextMinimum = new Edge(Integer.MAX_VALUE);
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Vertex nextVertex = this;
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Iterator<Map.Entry<Vertex,Edge>> it = edges.entrySet().iterator();
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while (it.hasNext()) {
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Map.Entry<Vertex,Edge> pair = it.next();
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if (!pair.getKey().isVisited()){
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if (!pair.getValue().isIncluded()) {
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if (pair.getValue().getWeight() < nextMinimum.getWeight()) {
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nextMinimum = pair.getValue();
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nextVertex = pair.getKey();
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}
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}
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}
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}
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return new Pair<>(nextVertex, nextMinimum);
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}
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public String originalToString(){
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StringBuilder sb = new StringBuilder();
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Iterator<Map.Entry<Vertex,Edge>> it = edges.entrySet().iterator();
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while (it.hasNext()) {
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Map.Entry<Vertex,Edge> pair = it.next();
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if (!pair.getValue().isPrinted()) {
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sb.append(getLabel());
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sb.append(" --- ");
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sb.append(pair.getValue().getWeight());
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sb.append(" --- ");
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sb.append(pair.getKey().getLabel());
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sb.append("\n");
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pair.getValue().setPrinted(true);
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}
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}
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return sb.toString();
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}
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public String includedToString(){
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StringBuilder sb = new StringBuilder();
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if (isVisited()) {
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Iterator<Map.Entry<Vertex,Edge>> it = edges.entrySet().iterator();
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while (it.hasNext()) {
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Map.Entry<Vertex,Edge> pair = it.next();
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if (pair.getValue().isIncluded()) {
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if (!pair.getValue().isPrinted()) {
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sb.append(getLabel());
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sb.append(" --- ");
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sb.append(pair.getValue().getWeight());
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sb.append(" --- ");
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sb.append(pair.getKey().getLabel());
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sb.append("\n");
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pair.getValue().setPrinted(true);
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}
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}
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}
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}
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return sb.toString();
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}
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}
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@ -0,0 +1,54 @@
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package com.baeldung.algorithms.prim;
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import java.util.ArrayList;
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import java.util.List;
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import org.junit.Test;
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public class PrimUnitTest {
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@Test
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public void givenAGraph_whenPrimRuns_thenPrintMST() {
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Prim prim = new Prim(createGraph());
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System.out.println(prim.originalGraphToString());
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System.out.println("----------------");
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prim.run();
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System.out.println();
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prim.resetPrintHistory();
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System.out.println(prim.minimumSpanningTreeToString());
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}
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public static List<Vertex> createGraph() {
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List<Vertex> graph = new ArrayList<>();
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Vertex a = new Vertex("A");
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Vertex b = new Vertex("B");
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Vertex c = new Vertex("C");
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Vertex d = new Vertex("D");
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Vertex e = new Vertex("E");
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Edge ab = new Edge(2);
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a.addEdge(b, ab);
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b.addEdge(a, ab);
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Edge ac = new Edge(3);
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a.addEdge(c, ac);
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c.addEdge(a, ac);
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Edge bc = new Edge(2);
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b.addEdge(c, bc);
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c.addEdge(b, bc);
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Edge be = new Edge(5);
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b.addEdge(e, be);
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e.addEdge(b, be);
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Edge cd = new Edge(1);
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c.addEdge(d, cd);
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d.addEdge(c, cd);
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Edge ce = new Edge(1);
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c.addEdge(e, ce);
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e.addEdge(c, ce);
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graph.add(a);
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graph.add(b);
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graph.add(c);
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graph.add(d);
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graph.add(e);
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return graph;
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}
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}
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