Add tests, remove main, improve docs in ExponentialSearch (TheAlgorithms#5664)

Author: Hardvan

DIRECTORY.md

@@ -1001,6 +1001,7 @@
             * [BM25InvertedIndexTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/BM25InvertedIndexTest.java)
             * [BreadthFirstSearchTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/BreadthFirstSearchTest.java)
             * [DepthFirstSearchTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/DepthFirstSearchTest.java)
+            * [ExponentialSearchTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/ExponentialSearchTest.java)
             * [FibonacciSearchTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/FibonacciSearchTest.java)
             * [HowManyTimesRotatedTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/HowManyTimesRotatedTest.java)
             * [KMPSearchTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/KMPSearchTest.java)

src/main/java/com/thealgorithms/searches/ExponentalSearch.java

@@ -2,44 +2,47 @@
 
 import com.thealgorithms.devutils.searches.SearchAlgorithm;
 import java.util.Arrays;
-import java.util.Random;
-import java.util.concurrent.ThreadLocalRandom;
-import java.util.stream.IntStream;
 
+/**
+ * ExponentialSearch is an algorithm that efficiently finds the position of a target
+ * value within a sorted array. It works by expanding the range to find the bounds
+ * where the target might exist and then using binary search within that range.
+ *
+ * <p>
+ * Worst-case time complexity: O(log n)
+ * Best-case time complexity: O(1) when the element is found at the first position.
+ * Average time complexity: O(log n)
+ * Worst-case space complexity: O(1)
+ * </p>
+ *
+ * <p>
+ * Note: This algorithm requires that the input array be sorted.
+ * </p>
+ */
 class ExponentialSearch implements SearchAlgorithm {
 
-    public static void main(String[] args) {
-        Random r = ThreadLocalRandom.current();
-
-        int size = 100;
-        int maxElement = 100000;
-
-        Integer[] integers = IntStream.generate(() -> r.nextInt(maxElement)).limit(size).sorted().boxed().toArray(Integer[] ::new);
-
-        // The element that should be found
-        int shouldBeFound = integers[r.nextInt(size - 1)];
-
-        ExponentialSearch search = new ExponentialSearch();
-        int atIndex = search.find(integers, shouldBeFound);
-
-        System.out.printf("Should be found: %d. Found %d at index %d. An array length %d%n", shouldBeFound, integers[atIndex], atIndex, size);
-
-        int toCheck = Arrays.binarySearch(integers, shouldBeFound);
-        System.out.printf("Found by system method at an index: %d. Is equal: %b%n", toCheck, toCheck == atIndex);
-    }
-
+    /**
+     * Finds the index of the specified key in a sorted array using exponential search.
+     *
+     * @param array The sorted array to search.
+     * @param key The element to search for.
+     * @param <T> The type of the elements in the array, which must be comparable.
+     * @return The index of the key if found, otherwise -1.
+     */
     @Override
     public <T extends Comparable<T>> int find(T[] array, T key) {
-        if (array[0] == key) {
+        if (array.length == 0) {
+            return -1;
+        }
+        if (array[0].equals(key)) {
             return 0;
         }
-        if (array[array.length - 1] == key) {
-            return array.length;
+        if (array[array.length - 1].equals(key)) {
+            return array.length - 1;
         }
 
         int range = 1;
-
-        while (range < array.length && array[range].compareTo(key) <= -1) {
+        while (range < array.length && array[range].compareTo(key) < 0) {
             range = range * 2;
         }
 

src/test/java/com/thealgorithms/searches/ExponentialSearchTest.java

@@ -0,0 +1,84 @@
+package com.thealgorithms.searches;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.stream.IntStream;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the ExponentialSearch class.
+ */
+class ExponentialSearchTest {
+
+    /**
+     * Test for basic exponential search functionality.
+     */
+    @Test
+    void testExponentialSearchFound() {
+        ExponentialSearch exponentialSearch = new ExponentialSearch();
+        Integer[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+        int key = 7;
+        int expectedIndex = 6; // Index of the key in the array
+        assertEquals(expectedIndex, exponentialSearch.find(array, key), "The index of the found element should be 6.");
+    }
+
+    /**
+     * Test for exponential search with the first element as the key.
+     */
+    @Test
+    void testExponentialSearchFirstElement() {
+        ExponentialSearch exponentialSearch = new ExponentialSearch();
+        Integer[] array = {1, 2, 3, 4, 5};
+        int key = 1; // First element
+        int expectedIndex = 0; // Index of the key in the array
+        assertEquals(expectedIndex, exponentialSearch.find(array, key), "The index of the first element should be 0.");
+    }
+
+    /**
+     * Test for exponential search with the last element as the key.
+     */
+    @Test
+    void testExponentialSearchLastElement() {
+        ExponentialSearch exponentialSearch = new ExponentialSearch();
+        Integer[] array = {1, 2, 3, 4, 5};
+        int key = 5; // Last element
+        int expectedIndex = 4; // Index of the key in the array
+        assertEquals(expectedIndex, exponentialSearch.find(array, key), "The index of the last element should be 4.");
+    }
+
+    /**
+     * Test for exponential search with a single element present.
+     */
+    @Test
+    void testExponentialSearchSingleElementFound() {
+        ExponentialSearch exponentialSearch = new ExponentialSearch();
+        Integer[] array = {1};
+        int key = 1; // Only element present
+        int expectedIndex = 0; // Index of the key in the array
+        assertEquals(expectedIndex, exponentialSearch.find(array, key), "The index of the single element should be 0.");
+    }
+
+    /**
+     * Test for exponential search with an empty array.
+     */
+    @Test
+    void testExponentialSearchEmptyArray() {
+        ExponentialSearch exponentialSearch = new ExponentialSearch();
+        Integer[] array = {}; // Empty array
+        int key = 1; // Key not present
+        int expectedIndex = -1; // Key not found
+        assertEquals(expectedIndex, exponentialSearch.find(array, key), "The element should not be found in an empty array.");
+    }
+
+    /**
+     * Test for exponential search on large array.
+     */
+    @Test
+    void testExponentialSearchLargeArray() {
+        ExponentialSearch exponentialSearch = new ExponentialSearch();
+        Integer[] array = IntStream.range(0, 10000).boxed().toArray(Integer[] ::new); // Array from 0 to 9999
+        int key = 9999;
+        int expectedIndex = 9999;
+        assertEquals(expectedIndex, exponentialSearch.find(array, key), "The index of the last element should be 9999.");
+    }
+}