Merge pull request #8222 from pazis/BAEL-3561

BAEL-3561 Prim's Algorithm

algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/prim/Edge.java

@@ -0,0 +1,36 @@
+package com.baeldung.algorithms.prim;
+
+public class Edge {
+
+    private int weight;
+    private boolean isIncluded = false;
+    private boolean isPrinted = false;
+
+    public Edge(int weight) {
+        this.weight = weight;
+    }
+
+    public int getWeight() {
+        return weight;
+    }
+
+    public void setWeight(int weight) {
+        this.weight = weight;
+    }
+
+    public boolean isIncluded() {
+        return isIncluded;
+    }
+
+    public void setIncluded(boolean included) {
+        isIncluded = included;
+    }
+
+    public boolean isPrinted() {
+        return isPrinted;
+    }
+
+    public void setPrinted(boolean printed) {
+        isPrinted = printed;
+    }
+}

algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/prim/Prim.java

@@ -0,0 +1,73 @@
+package com.baeldung.algorithms.prim;
+
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+
+import org.apache.commons.math3.util.Pair;
+
+public class Prim {
+
+    private List<Vertex> graph;
+
+    public Prim(List<Vertex> graph){
+        this.graph = graph;
+    }
+
+    public void run(){
+        if (graph.size() > 0){
+            graph.get(0).setVisited(true);
+        }
+        while (isDisconnected()){
+            Edge nextMinimum = new Edge(Integer.MAX_VALUE);
+            Vertex nextVertex = graph.get(0);
+            for (Vertex vertex : graph){
+                if (vertex.isVisited()){
+                    Pair<Vertex, Edge> candidate = vertex.nextMinimum();
+                    if (candidate.getValue().getWeight() < nextMinimum.getWeight()){
+                        nextMinimum = candidate.getValue();
+                        nextVertex = candidate.getKey();
+                    }
+                }
+            }
+            nextMinimum.setIncluded(true);
+            nextVertex.setVisited(true);
+        }
+    }
+
+    private boolean isDisconnected(){
+        for (Vertex vertex : graph){
+            if (!vertex.isVisited()){
+                return true;
+            }
+        }
+        return false;
+    }
+
+    public String originalGraphToString(){
+        StringBuilder sb = new StringBuilder();
+        for (Vertex vertex : graph){
+            sb.append(vertex.originalToString());
+        }
+        return sb.toString();
+    }
+
+    public void resetPrintHistory(){
+        for (Vertex vertex : graph){
+            Iterator<Map.Entry<Vertex,Edge>> it = vertex.getEdges().entrySet().iterator();
+            while (it.hasNext()) {
+                Map.Entry<Vertex,Edge> pair = it.next();
+                pair.getValue().setPrinted(false);
+            }
+        }
+    }
+
+    public String minimumSpanningTreeToString(){
+        StringBuilder sb = new StringBuilder();
+        for (Vertex vertex : graph){
+            sb.append(vertex.includedToString());
+        }
+        return sb.toString();
+    }
+
+}

algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/prim/Vertex.java

@@ -0,0 +1,106 @@
+package com.baeldung.algorithms.prim;
+
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
+
+import org.apache.commons.math3.util.Pair;
+
+public class Vertex {
+
+    private String label = null;
+    private Map<Vertex, Edge> edges = new HashMap<>();
+    private boolean isVisited = false;
+
+    public Vertex(String label){
+        this.label = label;
+    }
+
+    public String getLabel() {
+        return label;
+    }
+
+    public void setLabel(String label) {
+        this.label = label;
+    }
+
+    public Map<Vertex, Edge> getEdges() {
+        return edges;
+    }
+
+    public void addEdge(Vertex vertex, Edge edge){
+        if (this.edges.containsKey(vertex)){
+            if (edge.getWeight() < this.edges.get(vertex).getWeight()){
+                this.edges.replace(vertex, edge);
+            }
+        } else {
+            this.edges.put(vertex, edge);
+        }
+    }
+
+    public boolean isVisited() {
+        return isVisited;
+    }
+
+    public void setVisited(boolean visited) {
+        isVisited = visited;
+    }
+
+    public Pair<Vertex, Edge> nextMinimum(){
+        Edge nextMinimum = new Edge(Integer.MAX_VALUE);
+        Vertex nextVertex = this;
+        Iterator<Map.Entry<Vertex,Edge>> it = edges.entrySet().iterator();
+        while (it.hasNext()) {
+            Map.Entry<Vertex,Edge> pair = it.next();
+            if (!pair.getKey().isVisited()){
+                if (!pair.getValue().isIncluded()) {
+                    if (pair.getValue().getWeight() < nextMinimum.getWeight()) {
+                        nextMinimum = pair.getValue();
+                        nextVertex = pair.getKey();
+                    }
+                }
+            }
+        }
+        return new Pair<>(nextVertex, nextMinimum);
+    }
+
+    public String originalToString(){
+        StringBuilder sb = new StringBuilder();
+        Iterator<Map.Entry<Vertex,Edge>> it = edges.entrySet().iterator();
+        while (it.hasNext()) {
+            Map.Entry<Vertex,Edge> pair = it.next();
+            if (!pair.getValue().isPrinted()) {
+                sb.append(getLabel());
+                sb.append(" --- ");
+                sb.append(pair.getValue().getWeight());
+                sb.append(" --- ");
+                sb.append(pair.getKey().getLabel());
+                sb.append("\n");
+                pair.getValue().setPrinted(true);
+            }
+        }
+        return sb.toString();
+    }
+
+    public String includedToString(){
+        StringBuilder sb = new StringBuilder();
+        if (isVisited()) {
+            Iterator<Map.Entry<Vertex,Edge>> it = edges.entrySet().iterator();
+            while (it.hasNext()) {
+                Map.Entry<Vertex,Edge> pair = it.next();
+                if (pair.getValue().isIncluded()) {
+                    if (!pair.getValue().isPrinted()) {
+                        sb.append(getLabel());
+                        sb.append(" --- ");
+                        sb.append(pair.getValue().getWeight());
+                        sb.append(" --- ");
+                        sb.append(pair.getKey().getLabel());
+                        sb.append("\n");
+                        pair.getValue().setPrinted(true);
+                    }
+                }
+            }
+        }
+        return sb.toString();
+    }
+}

algorithms-miscellaneous-5/src/test/java/com/baeldung/algorithms/prim/PrimUnitTest.java

@@ -0,0 +1,54 @@
+package com.baeldung.algorithms.prim;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.Test;
+
+public class PrimUnitTest {
+
+    @Test
+    public void givenAGraph_whenPrimRuns_thenPrintMST() {
+        Prim prim = new Prim(createGraph());
+        System.out.println(prim.originalGraphToString());
+        System.out.println("----------------");
+        prim.run();
+        System.out.println();
+        prim.resetPrintHistory();
+        System.out.println(prim.minimumSpanningTreeToString());
+    }
+
+    public static List<Vertex> createGraph() {
+        List<Vertex> graph = new ArrayList<>();
+        Vertex a = new Vertex("A");
+        Vertex b = new Vertex("B");
+        Vertex c = new Vertex("C");
+        Vertex d = new Vertex("D");
+        Vertex e = new Vertex("E");
+        Edge ab = new Edge(2);
+        a.addEdge(b, ab);
+        b.addEdge(a, ab);
+        Edge ac = new Edge(3);
+        a.addEdge(c, ac);
+        c.addEdge(a, ac);
+        Edge bc = new Edge(2);
+        b.addEdge(c, bc);
+        c.addEdge(b, bc);
+        Edge be = new Edge(5);
+        b.addEdge(e, be);
+        e.addEdge(b, be);
+        Edge cd = new Edge(1);
+        c.addEdge(d, cd);
+        d.addEdge(c, cd);
+        Edge ce = new Edge(1);
+        c.addEdge(e, ce);
+        e.addEdge(c, ce);
+        graph.add(a);
+        graph.add(b);
+        graph.add(c);
+        graph.add(d);
+        graph.add(e);
+        return graph;
+    }
+
+}