fix(searches): require non-null arguments, update best-case complexity, and test UpperBound duplicates

Author: hardikkaurani

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

@@ -1,6 +1,7 @@
 package com.thealgorithms.searches;
 
 import com.thealgorithms.devutils.searches.SearchAlgorithm;
+import java.util.Objects;
 
 /**
  * The LowerBound method is used to return an index pointing to the first
@@ -13,7 +14,7 @@
  * This is an extension of BinarySearch.
  *
  * <p>
- * Worst-case performance O(log n) Best-case performance O(1) Average
+ * Worst-case performance O(log n) Best-case performance O(log n) Average
  * performance O(log n) Worst-case space complexity O(1)
  *
  * @author Pratik Padalia (https://github.com/15pratik)
@@ -26,11 +27,14 @@ class LowerBound implements SearchAlgorithm {
      * @param array is an array where the LowerBound value is to be found
      * @param key is an element for which the LowerBound is to be found
      * @param <T> is any comparable type
-     * @return index of the LowerBound element
+     * @return index of the first element not less than key, or 0 if array is empty
+     * @throws NullPointerException if {@code array} or {@code key} is null
      */
     @Override
     public <T extends Comparable<T>> int find(T[] array, T key) {
-        if (array == null || array.length == 0 || key == null) {
+        Objects.requireNonNull(array, "array must not be null");
+        Objects.requireNonNull(key, "key must not be null");
+        if (array.length == 0) {
             return 0;
         }
         return search(array, key, 0, array.length - 1);

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

@@ -1,6 +1,7 @@
 package com.thealgorithms.searches;
 
 import com.thealgorithms.devutils.searches.SearchAlgorithm;
+import java.util.Objects;
 
 /**
  * The UpperBound method is used to return an index pointing to the first
@@ -13,7 +14,7 @@
  * This is an extension of BinarySearch.
  *
  * <p>
- * Worst-case performance O(log n) Best-case performance O(1) Average
+ * Worst-case performance O(log n) Best-case performance O(log n) Average
  * performance O(log n) Worst-case space complexity O(1)
  *
  * @author Pratik Padalia (https://github.com/15pratik)
@@ -26,11 +27,14 @@ class UpperBound implements SearchAlgorithm {
      * @param array is an array where the UpperBound value is to be found
      * @param key is an element for which the UpperBound is to be found
      * @param <T> is any comparable type
-     * @return index of the UpperBound element
+     * @return index of the first element greater than key, last index if no such element exists, or 0 if array is empty
+     * @throws NullPointerException if {@code array} or {@code key} is null
      */
     @Override
     public <T extends Comparable<T>> int find(T[] array, T key) {
-        if (array == null || array.length == 0 || key == null) {
+        Objects.requireNonNull(array, "array must not be null");
+        Objects.requireNonNull(key, "key must not be null");
+        if (array.length == 0) {
             return 0;
         }
         return search(array, key, 0, array.length - 1);

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

@@ -1,6 +1,7 @@
 package com.thealgorithms.searches;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import org.junit.jupiter.api.Test;
 
@@ -80,7 +81,7 @@ void testLowerBoundNullAndEmptyEdgeCases() {
         LowerBound lowerBound = new LowerBound();
         Integer[] emptyArray = {};
         assertEquals(0, lowerBound.find(emptyArray, 5), "Lower bound for an empty array should be 0");
-        assertEquals(0, lowerBound.find(null, 5), "Lower bound for a null array should be 0");
-        assertEquals(0, lowerBound.find(new Integer[] {1, 2, 3}, null), "Lower bound for a null key should be 0");
+        assertThrows(NullPointerException.class, () -> lowerBound.find(null, 5));
+        assertThrows(NullPointerException.class, () -> lowerBound.find(new Integer[] {1, 2, 3}, null));
     }
 }

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

@@ -1,6 +1,7 @@
 package com.thealgorithms.searches;
 
 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 java.util.Random;
@@ -57,6 +58,15 @@ void testUpperBoundMultipleValues() {
         assertTrue(arrayWithDuplicates[index] > key, "Element at the upper bound index should be greater than the key.");
     }
 
+    @Test
+    void testUpperBoundDuplicates() {
+        Integer[] arrayWithDuplicates = {1, 2, 2, 2, 3};
+        assertEquals(4, upperBound.find(arrayWithDuplicates, 2), "Upper bound for 2 in {1, 2, 2, 2, 3} should be at index 4");
+
+        Integer[] allSame = {2, 2, 2, 2, 2};
+        assertEquals(4, upperBound.find(allSame, 2), "Upper bound for 2 in all-same array should be at last index 4");
+    }
+
     @Test
     void testUpperBoundLowerThanMin() {
         int key = 0; // Test with a key lower than the minimum element
@@ -99,7 +109,7 @@ void testUpperBoundSingleElementArray() {
 
     @Test
     void testUpperBoundNullArrayAndKey() {
-        assertEquals(0, upperBound.find(null, 5), "Upper bound for a null array should be 0.");
-        assertEquals(0, upperBound.find(new Integer[] {1, 2, 3}, null), "Upper bound for a null key should be 0.");
+        assertThrows(NullPointerException.class, () -> upperBound.find(null, 5));
+        assertThrows(NullPointerException.class, () -> upperBound.find(new Integer[] {1, 2, 3}, null));
     }
 }