Add BinarySearchStrings algorithm with comprehensive tests

Author: Jeevan Yewale

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

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+package com.thealgorithms.searches;
+
+/**
+ * Binary Search implementation specifically for String arrays
+ * This algorithm finds the position of a target string within a sorted string array
+ * 
+ * Time Complexity: O(log n * m) where n is array length and m is average string length
+ * Space Complexity: O(1)
+ * 
+ * @author Jeevan Yewale (https://github.com/JeevanYewale)
+ */
+public final class BinarySearchStrings {
+
+    private BinarySearchStrings() {
+        // Utility class
+    }
+
+    /**
+     * Performs binary search on a sorted string array
+     * 
+     * @param array sorted array of strings (must be sorted in lexicographical order)
+     * @param target the string to search for
+     * @return index of target string if found, -1 otherwise
+     */
+    public static int search(String[] array, String target) {
+        if (array == null || array.length == 0 || target == null) {
+            return -1;
+        }
+        
+        int left = 0;
+        int right = array.length - 1;
+        
+        while (left <= right) {
+            int mid = left + (right - left) / 2;
+            int comparison = target.compareTo(array[mid]);
+            
+            if (comparison == 0) {
+                return mid; // Found the target
+            } else if (comparison < 0) {
+                right = mid - 1; // Target is in left half
+            } else {
+                left = mid + 1; // Target is in right half
+            }
+        }
+        
+        return -1; // Target not found
+    }
+
+    /**
+     * Performs case-insensitive binary search on a sorted string array
+     * 
+     * @param array sorted array of strings (must be sorted in lexicographical order, case-insensitive)
+     * @param target the string to search for
+     * @return index of target string if found, -1 otherwise
+     */
+    public static int searchIgnoreCase(String[] array, String target) {
+        if (array == null || array.length == 0 || target == null) {
+            return -1;
+        }
+        
+        int left = 0;
+        int right = array.length - 1;
+        String targetLower = target.toLowerCase();
+        
+        while (left <= right) {
+            int mid = left + (right - left) / 2;
+            int comparison = targetLower.compareTo(array[mid].toLowerCase());
+            
+            if (comparison == 0) {
+                return mid; // Found the target
+            } else if (comparison < 0) {
+                right = mid - 1; // Target is in left half
+            } else {
+                left = mid + 1; // Target is in right half
+            }
+        }
+        
+        return -1; // Target not found
+    }
+}

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

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+package com.thealgorithms.searches;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test cases for BinarySearchStrings algorithm
+ * 
+ * @author Jeevan Yewale (https://github.com/JeevanYewale)
+ */
+class BinarySearchStringsTest {
+
+    @Test
+    void testBasicSearch() {
+        String[] array = {"apple", "banana", "cherry", "date", "elderberry"};
+        
+        assertEquals(0, BinarySearchStrings.search(array, "apple"));
+        assertEquals(2, BinarySearchStrings.search(array, "cherry"));
+        assertEquals(4, BinarySearchStrings.search(array, "elderberry"));
+        assertEquals(-1, BinarySearchStrings.search(array, "grape"));
+    }
+
+    @Test
+    void testEmptyArray() {
+        String[] array = {};
+        assertEquals(-1, BinarySearchStrings.search(array, "test"));
+    }
+
+    @Test
+    void testNullArray() {
+        assertEquals(-1, BinarySearchStrings.search(null, "test"));
+    }
+
+    @Test
+    void testNullTarget() {
+        String[] array = {"apple", "banana"};
+        assertEquals(-1, BinarySearchStrings.search(array, null));
+    }
+
+    @Test
+    void testSingleElement() {
+        String[] array = {"single"};
+        assertEquals(0, BinarySearchStrings.search(array, "single"));
+        assertEquals(-1, BinarySearchStrings.search(array, "other"));
+    }
+
+    @Test
+    void testCaseInsensitiveSearch() {
+        String[] array = {"apple", "banana", "cherry", "date", "elderberry"};
+        
+        assertEquals(0, BinarySearchStrings.searchIgnoreCase(array, "APPLE"));
+        assertEquals(2, BinarySearchStrings.searchIgnoreCase(array, "Cherry"));
+        assertEquals(-1, BinarySearchStrings.searchIgnoreCase(array, "GRAPE"));
+    }
+}