Merge branch 'master' into LIFOCache

Author: DenizAltunkapan

src/main/java/com/thealgorithms/matrix/MatrixMultiplication.java

@@ -0,0 +1,69 @@
+package com.thealgorithms.matrix;
+
+/**
+ * This class provides a method to perform matrix multiplication.
+ *
+ * <p>Matrix multiplication takes two 2D arrays (matrices) as input and
+ * produces their product, following the mathematical definition of
+ * matrix multiplication.
+ *
+ * <p>For more details:
+ * https://www.geeksforgeeks.org/java/java-program-to-multiply-two-matrices-of-any-size/
+ * https://en.wikipedia.org/wiki/Matrix_multiplication
+ *
+ * <p>Time Complexity: O(n^3) – where n is the dimension of the matrices
+ * (assuming square matrices for simplicity).
+ *
+ * <p>Space Complexity: O(n^2) – for storing the result matrix.
+ *
+ *
+ * @author Nishitha Wihala Pitigala
+ *
+ */
+
+public final class MatrixMultiplication {
+    private MatrixMultiplication() {
+    }
+
+    /**
+     * Multiplies two matrices.
+     *
+     * @param matrixA the first matrix rowsA x colsA
+     * @param matrixB the second matrix rowsB x colsB
+     * @return the product of the two matrices rowsA x colsB
+     * @throws IllegalArgumentException if the matrices cannot be multiplied
+     */
+    public static double[][] multiply(double[][] matrixA, double[][] matrixB) {
+        // Check the input matrices are not null
+        if (matrixA == null || matrixB == null) {
+            throw new IllegalArgumentException("Input matrices cannot be null");
+        }
+
+        // Check for empty matrices
+        if (matrixA.length == 0 || matrixB.length == 0 || matrixA[0].length == 0 || matrixB[0].length == 0) {
+            throw new IllegalArgumentException("Input matrices must not be empty");
+        }
+
+        // Validate the matrix dimensions
+        if (matrixA[0].length != matrixB.length) {
+            throw new IllegalArgumentException("Matrices cannot be multiplied: incompatible dimensions.");
+        }
+
+        int rowsA = matrixA.length;
+        int colsA = matrixA[0].length;
+        int colsB = matrixB[0].length;
+
+        // Initialize the result matrix with zeros
+        double[][] result = new double[rowsA][colsB];
+
+        // Perform matrix multiplication
+        for (int i = 0; i < rowsA; i++) {
+            for (int j = 0; j < colsB; j++) {
+                for (int k = 0; k < colsA; k++) {
+                    result[i][j] += matrixA[i][k] * matrixB[k][j];
+                }
+            }
+        }
+        return result;
+    }
+}

src/test/java/com/thealgorithms/datastructures/lists/SkipListTest.java

@@ -1,110 +1,115 @@
 package com.thealgorithms.datastructures.lists;
 
-import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 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.stream.IntStream;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
 
 class SkipListTest {
 
+    private SkipList<String> skipList;
+
+    @BeforeEach
+    void setUp() {
+        skipList = new SkipList<>();
+    }
+
     @Test
-    void add() {
-        SkipList<String> skipList = new SkipList<>();
+    @DisplayName("Add element and verify size and retrieval")
+    void testAdd() {
         assertEquals(0, skipList.size());
 
         skipList.add("value");
 
-        print(skipList);
         assertEquals(1, skipList.size());
+        assertEquals("value", skipList.get(0));
     }
 
     @Test
-    void get() {
-        SkipList<String> skipList = new SkipList<>();
+    @DisplayName("Get retrieves correct element by index")
+    void testGet() {
         skipList.add("value");
-
-        String actualValue = skipList.get(0);
-
-        print(skipList);
-        assertEquals("value", actualValue);
+        assertEquals("value", skipList.get(0));
     }
 
     @Test
-    void contains() {
-        SkipList<String> skipList = createSkipList();
-        print(skipList);
-
-        boolean contains = skipList.contains("b");
-
-        assertTrue(contains);
+    @DisplayName("Contains returns true if element exists")
+    void testContains() {
+        skipList = createSkipList();
+        assertTrue(skipList.contains("b"));
+        assertTrue(skipList.contains("a"));
+        assertFalse(skipList.contains("z")); // negative test
     }
 
     @Test
-    void removeFromHead() {
-        SkipList<String> skipList = createSkipList();
-        String mostLeftElement = skipList.get(0);
+    @DisplayName("Remove element from head and check size and order")
+    void testRemoveFromHead() {
+        skipList = createSkipList();
+        String first = skipList.get(0);
         int initialSize = skipList.size();
-        print(skipList);
 
-        skipList.remove(mostLeftElement);
+        skipList.remove(first);
 
-        print(skipList);
         assertEquals(initialSize - 1, skipList.size());
+        assertFalse(skipList.contains(first));
     }
 
     @Test
-    void removeFromTail() {
-        SkipList<String> skipList = createSkipList();
-        String mostRightValue = skipList.get(skipList.size() - 1);
+    @DisplayName("Remove element from tail and check size and order")
+    void testRemoveFromTail() {
+        skipList = createSkipList();
+        String last = skipList.get(skipList.size() - 1);
         int initialSize = skipList.size();
-        print(skipList);
 
-        skipList.remove(mostRightValue);
+        skipList.remove(last);
 
-        print(skipList);
         assertEquals(initialSize - 1, skipList.size());
+        assertFalse(skipList.contains(last));
     }
 
     @Test
-    void checkSortedOnLowestLayer() {
-        SkipList<String> skipList = new SkipList<>();
+    @DisplayName("Elements should be sorted at base level")
+    void testSortedOrderOnBaseLevel() {
         String[] values = {"d", "b", "a", "c"};
         Arrays.stream(values).forEach(skipList::add);
-        print(skipList);
 
         String[] actualOrder = IntStream.range(0, values.length).mapToObj(skipList::get).toArray(String[] ::new);
 
-        assertArrayEquals(new String[] {"a", "b", "c", "d"}, actualOrder);
+        org.junit.jupiter.api.Assertions.assertArrayEquals(new String[] {"a", "b", "c", "d"}, actualOrder);
     }
 
-    private SkipList<String> createSkipList() {
-        SkipList<String> skipList = new SkipList<>();
-        String[] values = {
-            "a",
-            "b",
-            "c",
-            "d",
-            "e",
-            "f",
-            "g",
-            "h",
-            "i",
-            "j",
-            "k",
-        };
+    @Test
+    @DisplayName("Duplicate elements can be added and count correctly")
+    void testAddDuplicates() {
+        skipList.add("x");
+        skipList.add("x");
+        assertEquals(2, skipList.size());
+        assertEquals("x", skipList.get(0));
+        assertEquals("x", skipList.get(1));
+    }
+
+    @Test
+    @DisplayName("Add multiple and remove all")
+    void testClearViaRemovals() {
+        String[] values = {"a", "b", "c"};
         Arrays.stream(values).forEach(skipList::add);
-        return skipList;
+
+        for (String v : values) {
+            skipList.remove(v);
+        }
+
+        assertEquals(0, skipList.size());
     }
 
-    /**
-     * Print Skip List representation to console.
-     * Optional method not involved in testing process. Used only for visualisation purposes.
-     * @param skipList to print
-     */
-    private void print(SkipList<?> skipList) {
-        System.out.println(skipList);
+    private SkipList<String> createSkipList() {
+        SkipList<String> s = new SkipList<>();
+        String[] values = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k"};
+        Arrays.stream(values).forEach(s::add);
+        return s;
     }
 }

src/test/java/com/thealgorithms/datastructures/queues/DequeTest.java

@@ -87,4 +87,38 @@ void testToString() {
         deque.addFirst(5);
         assertEquals("Head -> 5 <-> 10 <-> 20 <- Tail", deque.toString());
     }
+
+    @Test
+    void testAlternatingAddRemove() {
+        Deque<Integer> deque = new Deque<>();
+        deque.addFirst(1);
+        deque.addLast(2);
+        deque.addFirst(0);
+        assertEquals(0, deque.pollFirst());
+        assertEquals(2, deque.pollLast());
+        assertEquals(1, deque.pollFirst());
+        org.junit.jupiter.api.Assertions.assertTrue(deque.isEmpty());
+    }
+
+    @Test
+    void testSizeAfterOperations() {
+        Deque<Integer> deque = new Deque<>();
+        assertEquals(0, deque.size());
+        deque.addFirst(1);
+        deque.addLast(2);
+        deque.addFirst(3);
+        assertEquals(3, deque.size());
+        deque.pollFirst();
+        deque.pollLast();
+        assertEquals(1, deque.size());
+    }
+
+    @Test
+    void testNullValues() {
+        Deque<String> deque = new Deque<>();
+        deque.addFirst(null);
+        assertNull(deque.peekFirst());
+        assertNull(deque.pollFirst());
+        org.junit.jupiter.api.Assertions.assertTrue(deque.isEmpty());
+    }
 }

src/test/java/com/thealgorithms/matrix/MatrixMultiplicationTest.java

@@ -0,0 +1,101 @@
+package com.thealgorithms.matrix;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+public class MatrixMultiplicationTest {
+
+    private static final double EPSILON = 1e-9; // for floating point comparison
+
+    @Test
+    void testMultiply1by1() {
+        double[][] matrixA = {{1.0}};
+        double[][] matrixB = {{2.0}};
+        double[][] expected = {{2.0}};
+
+        double[][] result = MatrixMultiplication.multiply(matrixA, matrixB);
+        assertMatrixEquals(expected, result);
+    }
+
+    @Test
+    void testMultiply2by2() {
+        double[][] matrixA = {{1.0, 2.0}, {3.0, 4.0}};
+        double[][] matrixB = {{5.0, 6.0}, {7.0, 8.0}};
+        double[][] expected = {{19.0, 22.0}, {43.0, 50.0}};
+
+        double[][] result = MatrixMultiplication.multiply(matrixA, matrixB);
+        assertMatrixEquals(expected, result); // Use custom method due to floating point issues
+    }
+
+    @Test
+    void testMultiply3by2and2by1() {
+        double[][] matrixA = {{1.0, 2.0}, {3.0, 4.0}, {5.0, 6.0}};
+        double[][] matrixB = {{7.0}, {8.0}};
+        double[][] expected = {{23.0}, {53.0}, {83.0}};
+
+        double[][] result = MatrixMultiplication.multiply(matrixA, matrixB);
+        assertMatrixEquals(expected, result);
+    }
+
+    @Test
+    void testMultiplyNonRectangularMatrices() {
+        double[][] matrixA = {{1.0, 2.0, 3.0}, {4.0, 5.0, 6.0}};
+        double[][] matrixB = {{7.0, 8.0}, {9.0, 10.0}, {11.0, 12.0}};
+        double[][] expected = {{58.0, 64.0}, {139.0, 154.0}};
+
+        double[][] result = MatrixMultiplication.multiply(matrixA, matrixB);
+        assertMatrixEquals(expected, result);
+    }
+
+    @Test
+    void testNullMatrixA() {
+        double[][] b = {{1, 2}, {3, 4}};
+        assertThrows(IllegalArgumentException.class, () -> MatrixMultiplication.multiply(null, b));
+    }
+
+    @Test
+    void testNullMatrixB() {
+        double[][] a = {{1, 2}, {3, 4}};
+        assertThrows(IllegalArgumentException.class, () -> MatrixMultiplication.multiply(a, null));
+    }
+
+    @Test
+    void testMultiplyNull() {
+        double[][] matrixA = {{1.0, 2.0}, {3.0, 4.0}};
+        double[][] matrixB = null;
+
+        Exception exception = assertThrows(IllegalArgumentException.class, () -> MatrixMultiplication.multiply(matrixA, matrixB));
+
+        String expectedMessage = "Input matrices cannot be null";
+        String actualMessage = exception.getMessage();
+
+        assertTrue(actualMessage.contains(expectedMessage));
+    }
+
+    @Test
+    void testIncompatibleDimensions() {
+        double[][] a = {{1.0, 2.0}};
+        double[][] b = {{1.0, 2.0}};
+        assertThrows(IllegalArgumentException.class, () -> MatrixMultiplication.multiply(a, b));
+    }
+
+    @Test
+    void testEmptyMatrices() {
+        double[][] a = new double[0][0];
+        double[][] b = new double[0][0];
+        assertThrows(IllegalArgumentException.class, () -> MatrixMultiplication.multiply(a, b));
+    }
+
+    private void assertMatrixEquals(double[][] expected, double[][] actual) {
+        assertEquals(expected.length, actual.length, "Row count mismatch");
+        for (int i = 0; i < expected.length; i++) {
+            assertEquals(expected[i].length, actual[i].length, "Column count mismatch at row " + i);
+            for (int j = 0; j < expected[i].length; j++) {
+                assertEquals(expected[i][j], actual[i][j], EPSILON, "Mismatch at (" + i + "," + j + ")");
+            }
+        }
+    }
+}