Merge pull request #5782 from kcacademic/graphs-java

BAEL-2334: Adding file for the tutorial on Graph in Java

Author: lor6

core-java/src/main/java/com/baeldung/graph/Graph.java

@@ -0,0 +1,76 @@
+package com.baeldung.graph;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+public class Graph {
+    private Map<Vertex, List<Vertex>> adjVertices;
+
+    Graph() {
+        this.adjVertices = new HashMap<Vertex, List<Vertex>>();
+    }
+
+    void addVertex(String label) {
+        adjVertices.putIfAbsent(new Vertex(label), new ArrayList<>());
+    }
+
+    void removeVertex(String label) {
+        Vertex v = new Vertex(label);
+        adjVertices.values().stream().map(e -> e.remove(v)).collect(Collectors.toList());
+        adjVertices.remove(new Vertex(label));
+    }
+
+    void addEdge(String label1, String label2) {
+        Vertex v1 = new Vertex(label1);
+        Vertex v2 = new Vertex(label2);
+        adjVertices.get(v1).add(v2);
+        adjVertices.get(v2).add(v1);
+    }
+
+    void removeEdge(String label1, String label2) {
+        Vertex v1 = new Vertex(label1);
+        Vertex v2 = new Vertex(label2);
+        List<Vertex> eV1 = adjVertices.get(v1);
+        List<Vertex> eV2 = adjVertices.get(v2);
+        if (eV1 != null)
+            eV1.remove(v2);
+        if (eV2 != null)
+            eV2.remove(v1);
+    }
+
+    List<Vertex> getAdjVertices(String label) {
+        return adjVertices.get(new Vertex(label));
+    }
+    
+    String printGraph() {
+        StringBuffer sb = new StringBuffer();
+        for(Vertex v : adjVertices.keySet()) {
+            sb.append(v);
+            sb.append(adjVertices.get(v));
+        }
+        return sb.toString();
+    }
+
+    class Vertex {
+        String label;
+        Vertex(String label) {
+            this.label = label;
+        }
+        @Override
+        public boolean equals(Object obj) {
+            Vertex vertex = (Vertex) obj;
+            return vertex.label == label;
+        }
+        @Override
+        public int hashCode() {
+            return label.hashCode();
+        }
+        @Override
+        public String toString() {
+            return label;
+        }
+    }
+}

core-java/src/main/java/com/baeldung/graph/GraphTraversal.java

@@ -0,0 +1,44 @@
+package com.baeldung.graph;
+
+import java.util.LinkedHashSet;
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.Set;
+import java.util.Stack;
+
+import com.baeldung.graph.Graph.Vertex;
+
+public class GraphTraversal {
+    static Set<String> depthFirstTraversal(Graph graph, String root) {
+        Set<String> visited = new LinkedHashSet<String>();
+        Stack<String> stack = new Stack<String>();
+        stack.push(root);
+        while (!stack.isEmpty()) {
+            String vertex = stack.pop();
+            if (!visited.contains(vertex)) {
+                visited.add(vertex);
+                for (Vertex v : graph.getAdjVertices(vertex)) {              
+                    stack.push(v.label);
+                }
+            }
+        }
+        return visited;
+    }
+
+    static Set<String> breadthFirstTraversal(Graph graph, String root) {
+        Set<String> visited = new LinkedHashSet<String>();
+        Queue<String> queue = new LinkedList<String>();
+        queue.add(root);
+        visited.add(root);
+        while (!queue.isEmpty()) {
+            String vertex = queue.poll();
+            for (Vertex v : graph.getAdjVertices(vertex)) {
+                if (!visited.contains(v.label)) {
+                    visited.add(v.label);
+                    queue.add(v.label);
+                }
+            }
+        }
+        return visited;
+    }
+}

core-java/src/test/java/com/baeldung/graph/GraphTraversalUnitTest.java

@@ -0,0 +1,36 @@
+package com.baeldung.graph;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class GraphTraversalUnitTest {
+    @Test
+    public void givenAGraph_whenTraversingDepthFirst_thenExpectedResult() {
+        Graph graph = createGraph();
+        Assert.assertEquals("[Bob, Rob, Maria, Alice, Mark]", 
+            GraphTraversal.depthFirstTraversal(graph, "Bob").toString());
+    }
+    
+    @Test
+    public void givenAGraph_whenTraversingBreadthFirst_thenExpectedResult() {
+        Graph graph = createGraph();
+        Assert.assertEquals("[Bob, Alice, Rob, Mark, Maria]", 
+            GraphTraversal.breadthFirstTraversal(graph, "Bob").toString());
+    }
+    
+    Graph createGraph() {
+        Graph graph = new Graph();
+        graph.addVertex("Bob");
+        graph.addVertex("Alice");
+        graph.addVertex("Mark");
+        graph.addVertex("Rob");
+        graph.addVertex("Maria");
+        graph.addEdge("Bob", "Alice");
+        graph.addEdge("Bob", "Rob");
+        graph.addEdge("Alice", "Mark");
+        graph.addEdge("Rob", "Mark");
+        graph.addEdge("Alice", "Maria");
+        graph.addEdge("Rob", "Maria");
+        return graph;
+    }
+}