Add tests, remove main, fix bug in Sparsity

DIRECTORY.md

@@ -995,6 +995,7 @@
             * [MedianOfRunningArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MedianOfRunningArrayTest.java)
             * [MirrorOfMatrixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MirrorOfMatrixTest.java)
             * [PalindromeSinglyLinkedListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/PalindromeSinglyLinkedListTest.java)
+            * [SparsityTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/SparsityTest.java)
             * [TwoSumProblemTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/TwoSumProblemTest.java)
           * others
             * [ArrayLeftRotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/ArrayLeftRotationTest.java)

src/main/java/com/thealgorithms/misc/Sparsity.java

@@ -1,7 +1,5 @@
 package com.thealgorithms.misc;
 
-import java.util.Scanner;
-
 /*
  *A matrix is sparse if many of its coefficients are zero (In general if 2/3rd of matrix elements
  *are 0, it is considered as sparse). The interest in sparsity arises because its exploitation can
@@ -22,6 +20,10 @@ private Sparsity() {
      *
      */
     static double sparsity(double[][] mat) {
+        if (mat == null || mat.length == 0) {
+            throw new IllegalArgumentException("Matrix cannot be null or empty");
+        }
+
         int zero = 0;
         // Traversing the matrix to count number of zeroes
         for (int i = 0; i < mat.length; i++) {
@@ -32,25 +34,6 @@ static double sparsity(double[][] mat) {
             }
         }
         // return sparsity
-        return ((double) zero / (mat.length * mat[1].length));
-    }
-
-    // Driver method
-    public static void main(String[] args) {
-        Scanner in = new Scanner(System.in);
-        System.out.println("Enter number of rows in matrix: ");
-        int n = in.nextInt();
-        System.out.println("Enter number of Columns in matrix: ");
-        int m = in.nextInt();
-
-        System.out.println("Enter Matrix elements: ");
-        double[][] mat = new double[n][m];
-        for (int i = 0; i < n; i++) {
-            for (int j = 0; j < m; j++) {
-                mat[i][j] = in.nextDouble();
-            }
-        }
-        System.out.println("Sparsity of matrix is: " + sparsity(mat));
-        in.close();
+        return ((double) zero / (mat.length * mat[0].length));
     }
 }

src/test/java/com/thealgorithms/misc/SparsityTest.java

@@ -0,0 +1,66 @@
+package com.thealgorithms.misc;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+public class SparsityTest {
+
+    private static final double DELTA = 1e-9;
+
+    @Test
+    public void testAllZeroElements() {
+        double[][] mat = {{0, 0, 0}, {0, 0, 0}, {0, 0, 0}};
+        double expectedSparsity = 1.0;
+        assertEquals(expectedSparsity, Sparsity.sparsity(mat), DELTA, "Sparsity of a matrix with all zero elements should be 1.0");
+    }
+
+    @Test
+    public void testNoZeroElements() {
+        double[][] mat = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
+        double expectedSparsity = 0.0;
+        assertEquals(expectedSparsity, Sparsity.sparsity(mat), DELTA, "Sparsity of a matrix with no zero elements should be 0.0");
+    }
+
+    @Test
+    public void testMixedElements() {
+        double[][] mat = {{0, 2, 0}, {4, 0, 6}, {0, 8, 0}};
+        double expectedSparsity = 5.0 / 9.0;
+        assertEquals(expectedSparsity, Sparsity.sparsity(mat), DELTA, "Sparsity of the matrix should be 5/9");
+    }
+
+    @Test
+    public void testSingleRowMatrix() {
+        double[][] mat = {{0, 1, 0, 2, 0}};
+        double expectedSparsity = 3.0 / 5.0;
+        assertEquals(expectedSparsity, Sparsity.sparsity(mat), DELTA, "Sparsity of the single-row matrix should be 3/5");
+    }
+
+    @Test
+    public void testSingleColumnMatrix() {
+        double[][] mat = {{1}, {0}, {0}, {2}};
+        double expectedSparsity = 2.0 / 4.0;
+        assertEquals(expectedSparsity, Sparsity.sparsity(mat), DELTA, "Sparsity of the single-column matrix should be 2/4");
+    }
+
+    @Test
+    public void testEmptyMatrix() {
+        double[][] mat = {};
+        assertThrows(IllegalArgumentException.class, () -> Sparsity.sparsity(mat), "Sparsity of an empty matrix should throw an IllegalArgumentException");
+    }
+
+    @Test
+    public void testMatrixWithSingleElementZero() {
+        double[][] mat = {{0}};
+        double expectedSparsity = 1.0;
+        assertEquals(expectedSparsity, Sparsity.sparsity(mat), DELTA, "Sparsity of a matrix with a single zero element should be 1.0");
+    }
+
+    @Test
+    public void testMatrixWithSingleElementNonZero() {
+        double[][] mat = {{5}};
+        double expectedSparsity = 0.0;
+        assertEquals(expectedSparsity, Sparsity.sparsity(mat), DELTA, "Sparsity of a matrix with a single non-zero element should be 0.0");
+    }
+}