refactor: Add tests, fix removeEdge bug in MatrixGraphs

DIRECTORY.md

@@ -811,6 +811,7 @@
               * [HamiltonianCycleTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/HamiltonianCycleTest.java)
               * [JohnsonsAlgorithmTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/JohnsonsAlgorithmTest.java)
               * [KosarajuTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/KosarajuTest.java)
+              * [MatrixGraphsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/MatrixGraphsTest.java)
               * [TarjansAlgorithmTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/TarjansAlgorithmTest.java)
               * [WelshPowellTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/graphs/WelshPowellTest.java)
             * hashmap

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

@@ -102,7 +102,7 @@ public int numberOfVertices() {
     /**
      * Updates the number of edges in the graph
      *
-     * @param newNumberOfEdges
+     * @param newNumberOfEdges the new number of edges
      *
      */
     private void setNumberOfEdges(int newNumberOfEdges) {
@@ -202,7 +202,7 @@ public boolean addEdge(int from, int to) {
      * exists and is removed
      */
     public boolean removeEdge(int from, int to) {
-        if (!this.vertexDoesExist(from) || !this.vertexDoesExist(to)) {
+        if (this.vertexDoesExist(from) && this.vertexDoesExist(to)) {
             if (this.adjacencyOfEdgeDoesExist(from, to)) {
                 this.adjacency()[from][to] = AdjacencyMatrixGraph.EDGE_NONE;
                 this.adjacency()[to][from] = AdjacencyMatrixGraph.EDGE_NONE;
@@ -223,14 +223,14 @@ public boolean removeEdge(int from, int to) {
     public List<Integer> depthFirstOrder(int startVertex) {
         // If the startVertex is invalid, return an empty list
         if (startVertex >= vertexCount || startVertex < 0) {
-            return new ArrayList<Integer>();
+            return new ArrayList<>();
         }
 
         // Create an array to track the visited vertices
         boolean[] visited = new boolean[vertexCount];
 
         // Create a list to keep track of the order of our traversal
-        ArrayList<Integer> orderList = new ArrayList<Integer>();
+        ArrayList<Integer> orderList = new ArrayList<>();
 
         // Perform our DFS algorithm
         depthFirstOrder(startVertex, visited, orderList);
@@ -278,18 +278,18 @@ private void depthFirstOrder(int currentVertex, boolean[] visited, List<Integer>
     public List<Integer> breadthFirstOrder(int startVertex) {
         // If the specified startVertex is invalid, return an empty list
         if (startVertex >= vertexCount || startVertex < 0) {
-            return new ArrayList<Integer>();
+            return new ArrayList<>();
         }
 
         // Create an array to keep track of the visited vertices
         boolean[] visited = new boolean[vertexCount];
 
         // Create a list to keep track of the ordered vertices
-        ArrayList<Integer> orderList = new ArrayList<Integer>();
+        ArrayList<Integer> orderList = new ArrayList<>();
 
         // Create a queue for our BFS algorithm and add the startVertex
         // to the queue
-        Queue<Integer> queue = new LinkedList<Integer>();
+        Queue<Integer> queue = new LinkedList<>();
         queue.add(startVertex);
 
         // Continue until the queue is empty
@@ -327,19 +327,19 @@ public List<Integer> breadthFirstOrder(int startVertex) {
      * @return returns a string describing this graph
      */
     public String toString() {
-        String s = "    ";
+        StringBuilder s = new StringBuilder("    ");
         for (int i = 0; i < this.numberOfVertices(); i++) {
-            s = s + i + " ";
+            s.append(i).append(" ");
         }
-        s = s + " \n";
+        s.append(" \n");
 
         for (int i = 0; i < this.numberOfVertices(); i++) {
-            s = s + i + " : ";
+            s.append(i).append(" : ");
             for (int j = 0; j < this.numberOfVertices(); j++) {
-                s = s + this.adjMatrix[i][j] + " ";
+                s.append(this.adjMatrix[i][j]).append(" ");
             }
-            s = s + "\n";
+            s.append("\n");
         }
-        return s;
+        return s.toString();
     }
 }

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

@@ -0,0 +1,140 @@
+package com.thealgorithms.datastructures.graphs;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.Arrays;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class MatrixGraphsTest {
+
+    @Test
+    void testGraphConstruction() {
+        AdjacencyMatrixGraph graph = new AdjacencyMatrixGraph(5);
+        assertEquals(5, graph.numberOfVertices());
+        assertEquals(0, graph.numberOfEdges());
+    }
+
+    @Test
+    void testAddEdge() {
+        AdjacencyMatrixGraph graph = new AdjacencyMatrixGraph(5);
+        assertTrue(graph.addEdge(0, 1));
+        assertTrue(graph.edgeDoesExist(0, 1));
+        assertTrue(graph.edgeDoesExist(1, 0));
+        assertEquals(1, graph.numberOfEdges());
+
+        // Adding the same edge again should return false
+        assertFalse(graph.addEdge(0, 1));
+        assertFalse(graph.addEdge(5, 1));
+        assertFalse(graph.addEdge(-1, 1));
+    }
+
+    @Test
+    void testRemoveEdge() {
+        AdjacencyMatrixGraph graph = new AdjacencyMatrixGraph(5);
+        graph.addEdge(0, 1);
+        graph.addEdge(1, 2);
+
+        assertTrue(graph.removeEdge(0, 1));
+        assertFalse(graph.edgeDoesExist(0, 1));
+        assertFalse(graph.edgeDoesExist(1, 0));
+        assertEquals(1, graph.numberOfEdges());
+
+        assertFalse(graph.removeEdge(0, 3));
+        assertFalse(graph.removeEdge(5, 1));
+        assertFalse(graph.removeEdge(-1, 1));
+    }
+
+    @Test
+    void testVertexDoesExist() {
+        AdjacencyMatrixGraph graph = new AdjacencyMatrixGraph(5);
+        assertTrue(graph.vertexDoesExist(0));
+        assertTrue(graph.vertexDoesExist(4));
+        assertFalse(graph.vertexDoesExist(5));
+        assertFalse(graph.vertexDoesExist(-1));
+    }
+
+    @Test
+    void testDepthFirstOrder() {
+        AdjacencyMatrixGraph graph = new AdjacencyMatrixGraph(5);
+        graph.addEdge(0, 1);
+        graph.addEdge(0, 2);
+        graph.addEdge(1, 3);
+        graph.addEdge(2, 4);
+
+        List<Integer> dfs = graph.depthFirstOrder(0);
+        assertEquals(5, dfs.size());
+        assertEquals(0, dfs.getFirst());
+
+        assertTrue(dfs.containsAll(Arrays.asList(0, 1, 2, 3, 4)));
+
+        List<Integer> emptyDfs = graph.depthFirstOrder(5);
+        assertTrue(emptyDfs.isEmpty());
+    }
+
+    @Test
+    void testBreadthFirstOrder() {
+        AdjacencyMatrixGraph graph = new AdjacencyMatrixGraph(5);
+        graph.addEdge(0, 1);
+        graph.addEdge(0, 2);
+        graph.addEdge(1, 3);
+        graph.addEdge(2, 4);
+
+        List<Integer> bfs = graph.breadthFirstOrder(0);
+        assertEquals(5, bfs.size());
+        assertEquals(0, bfs.getFirst());
+
+        assertTrue(bfs.containsAll(Arrays.asList(0, 1, 2, 3, 4)));
+
+        List<Integer> emptyBfs = graph.breadthFirstOrder(5);
+        assertTrue(emptyBfs.isEmpty());
+    }
+
+    @Test
+    void testToString() {
+        AdjacencyMatrixGraph graph = new AdjacencyMatrixGraph(3);
+        graph.addEdge(0, 1);
+        graph.addEdge(1, 2);
+
+        String expected = "    0 1 2  \n"
+            + "0 : 0 1 0 \n"
+            + "1 : 1 0 1 \n"
+            + "2 : 0 1 0 \n";
+
+        assertEquals(expected, graph.toString());
+    }
+
+    @Test
+    void testCyclicGraph() {
+        AdjacencyMatrixGraph graph = new AdjacencyMatrixGraph(4);
+        graph.addEdge(0, 1);
+        graph.addEdge(1, 2);
+        graph.addEdge(2, 3);
+        graph.addEdge(3, 0);
+
+        List<Integer> dfs = graph.depthFirstOrder(0);
+        List<Integer> bfs = graph.breadthFirstOrder(0);
+
+        assertEquals(4, dfs.size());
+        assertEquals(4, bfs.size());
+        assertTrue(dfs.containsAll(Arrays.asList(0, 1, 2, 3)));
+        assertTrue(bfs.containsAll(Arrays.asList(0, 1, 2, 3)));
+    }
+
+    @Test
+    void testDisconnectedGraph() {
+        AdjacencyMatrixGraph graph = new AdjacencyMatrixGraph(5);
+        graph.addEdge(0, 1);
+        graph.addEdge(2, 3);
+
+        List<Integer> dfs = graph.depthFirstOrder(0);
+        List<Integer> bfs = graph.breadthFirstOrder(0);
+
+        assertEquals(2, dfs.size());
+        assertEquals(2, bfs.size());
+        assertTrue(dfs.containsAll(Arrays.asList(0, 1)));
+        assertTrue(bfs.containsAll(Arrays.asList(0, 1)));
+    }
+}