initial commit for MultistageGraph.java & MultistageGraphTest.java

Author: GouthamGuna

src/main/java/com/thealgorithms/datastructures/graphs/MultistageGraph.java

@@ -0,0 +1,74 @@
+package com.thealgorithms.datastructures.graphs;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public final class MultistageGraph {
+    
+    private MultistageGraph() {
+        
+    }
+     private int k; // number of partitions (k > 2)
+
+    // Adjacency list to store edges between different stages
+    public List<List<Integer>> adjacencyList;
+
+    public MultistageGraph(int k) {
+        this.k = k;
+        this.adjacencyList = new ArrayList<>();
+
+        // Initialize the adjacency list with empty lists for each stage
+        for (int i = 0; i < k; i++) {
+            adjacencyList.add(new ArrayList<>());
+        }
+    }
+
+    public void addEdge(int fromStage, int toStage) throws IllegalArgumentException {
+        if (!isValidStageNumber(fromStage)) {
+            throw new IllegalArgumentException("Invalid stage number: " + fromStage);
+        }
+
+        if (!isValidStageNumber(toStage)) {
+            throw new IllegalArgumentException("Invalid stage number: " + toStage);
+        }
+
+        // Check if the edge exists between the given stages, and add it if not
+        if (adjacencyList.get(fromStage - 1).contains(toStage)) {
+            System.out.println("Edge already exists between stage " + fromStage + " and stage " + toStage);
+        } else {
+            adjacencyList.get(fromStage - 1).add(toStage);
+            System.out.println("Added edge between stage " + fromStage + " and stage " + toStage);
+        }
+    }
+
+    private boolean isValidStageNumber(int stage) {
+        return (stage >= 1 && stage <= k);
+    }
+
+    public void printGraph() {
+        System.out.println("Multistage Graph:");
+
+        for (int i = 0; i < k; i++) {
+            System.out.print(i + " -> ");
+
+            for (Integer adjacentStage : adjacencyList.get(i)) {
+                if (!adjacentStage.equals(i)) {
+                    System.out.println(" -> " + adjacentStage);
+                }
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        MultistageGraph graph = new MultistageGraph(4); // Create a multistage graph with k = 4 partitions
+
+        try {
+            graph.addEdge(1, 2);
+            graph.addEdge(1, 3);
+            graph.addEdge(2, 3);
+            graph.printGraph();
+        } catch (IllegalArgumentException e) {
+            System.out.println("Error: " + e.getMessage());
+        }
+    }
+}

src/test/java/com/thealgorithms/datastructures/graphs/MultistageGraphTest.java

@@ -0,0 +1,53 @@
+package com.thealgorithms.datastructures.graphs;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+public class MultistageGraphTest {
+
+@Test
+public void testAddEdge_invalidFromStage() {
+    MultistageGraph graph = new MultistageGraph(3);
+
+    assertThrows(IllegalArgumentException.class, () -> graph.addEdge(0, 2));
+}
+
+@Test
+public void testAddEdge_invalidToStage() {
+    MultistageGraph graph = new MultistageGraph(3);
+
+    assertThrows(IllegalArgumentException.class, () -> graph.addEdge(1, 4));
+}
+
+@Test
+public void testAddEdge_edgeAlreadyExists() {
+    MultistageGraph graph = new MultistageGraph(3);
+
+    graph.addEdge(1, 2);
+    graph.addEdge(1, 2); // Attempt to add the same edge again
+
+    List<Integer> expectedAdjacentStages = Arrays.asList(2);
+    assertEquals(expectedAdjacentStages, graph.adjacencyList.get(0));
+}
+
+@Test
+public void testAddEdge_printsSuccessMessage() {
+    MultistageGraph graph = new MultistageGraph(3);
+
+    // Capture the standard output stream
+    ByteArrayOutputStream outputStreamCaptor = new ByteArrayOutputStream();
+    System.setOut(new PrintStream(outputStreamCaptor));
+
+    graph.addEdge(1, 2);
+
+    String expectedOutput = "Added edge between stage 1 and stage 2\r\n";
+    assertEquals(expectedOutput, outputStreamCaptor.toString());
+}
+}