Fix out-of-bounds access and identity comparison in FibonacciSearch

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

@@ -69,7 +69,7 @@ public <T extends Comparable<T>> int find(T[] array, T key) {
             }
         }
 
-        if (fibMinus1 == 1 && array[offset + 1] == key) {
+        if (fibMinus1 == 1 && offset + 1 < n && array[offset + 1].compareTo(key) == 0) {
             return offset + 1;
         }
 

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

@@ -121,4 +121,53 @@ void testFibonacciSearchLargeArray() {
         int expectedIndex = 9999;
         assertEquals(expectedIndex, fibonacciSearch.find(array, key), "The index of the last element should be 9999.");
     }
+
+    /**
+     * A key greater than every element used to throw {@link ArrayIndexOutOfBoundsException},
+     * because the final probe read {@code array[offset + 1]} without checking the bound.
+     */
+    @Test
+    void testFibonacciSearchKeyGreaterThanLastElement() {
+        FibonacciSearch fibonacciSearch = new FibonacciSearch();
+        for (int length = 1; length <= 50; length++) {
+            Integer[] array = new Integer[length];
+            for (int i = 0; i < length; i++) {
+                array[i] = i;
+            }
+            assertEquals(-1, fibonacciSearch.find(array, length), "A key above the maximum should not be found for length " + length + ".");
+        }
+    }
+
+    /**
+     * The final probe used reference equality, so a key that is equal but not identical to the
+     * stored element was reported as missing. Values above 127 are outside the {@link Integer}
+     * cache and therefore are not the same object as the boxed array element.
+     */
+    @Test
+    void testFibonacciSearchFindsEqualButNotIdenticalKey() {
+        FibonacciSearch fibonacciSearch = new FibonacciSearch();
+        Integer[] array = {10, 20, 300};
+        assertEquals(2, fibonacciSearch.find(array, Integer.valueOf(300)), "The index of the found element should be 2.");
+
+        String[] words = {"a", "b", "c"};
+        String equalButDistinct = new StringBuilder("c").toString();
+        assertEquals(2, fibonacciSearch.find(words, equalButDistinct), "The index of the found element should be 2.");
+    }
+
+    /**
+     * Every element must be found regardless of the array length.
+     */
+    @Test
+    void testFibonacciSearchFindsEveryElement() {
+        FibonacciSearch fibonacciSearch = new FibonacciSearch();
+        for (int length = 1; length <= 50; length++) {
+            Integer[] array = new Integer[length];
+            for (int i = 0; i < length; i++) {
+                array[i] = 1000 + i * 2;
+            }
+            for (int i = 0; i < length; i++) {
+                assertEquals(i, fibonacciSearch.find(array, Integer.valueOf(1000 + i * 2)), "Element at index " + i + " should be found for length " + length + ".");
+            }
+        }
+    }
 }