Add BTree implementation (#6248)

src/test/java/com/thealgorithms/datastructures/trees/BTreeTest.java

@@ -0,0 +1,94 @@
+package com.thealgorithms.datastructures.trees;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import org.junit.jupiter.api.Test;
+
+public class BTreeTest {
+
+    @Test
+    public void testInsertSearchDelete() {
+        BTree bTree = new BTree(3); // Minimum degree t = 3
+
+        int[] values = {10, 20, 5, 6, 12, 30, 7, 17};
+        for (int val : values) {
+            bTree.insert(val);
+        }
+
+        for (int val : values) {
+            assertTrue(bTree.search(val), "Should find inserted value: " + val);
+        }
+
+        ArrayList<Integer> traversal = new ArrayList<>();
+        bTree.traverse(traversal);
+        assertEquals(Arrays.asList(5, 6, 7, 10, 12, 17, 20, 30), traversal);
+
+        bTree.delete(6);
+        assertFalse(bTree.search(6));
+        traversal.clear();
+        bTree.traverse(traversal);
+        assertEquals(Arrays.asList(5, 7, 10, 12, 17, 20, 30), traversal);
+    }
+
+    @Test
+    public void testEmptyTreeSearch() {
+        BTree bTree = new BTree(3);
+        assertFalse(bTree.search(42), "Search in empty tree should return false.");
+    }
+
+    @Test
+    public void testDuplicateInsertions() {
+        BTree bTree = new BTree(3);
+        bTree.insert(15);
+        bTree.insert(15); // Attempt duplicate
+        bTree.insert(15); // Another duplicate
+
+        ArrayList<Integer> traversal = new ArrayList<>();
+        bTree.traverse(traversal);
+
+        // Should contain only one 15
+        long count = traversal.stream().filter(x -> x == 15).count();
+        assertEquals(1, count, "Duplicate keys should not be inserted.");
+    }
+
+    @Test
+    public void testDeleteNonExistentKey() {
+        BTree bTree = new BTree(3);
+        bTree.insert(10);
+        bTree.insert(20);
+        bTree.delete(99); // Doesn't exist
+        assertTrue(bTree.search(10));
+        assertTrue(bTree.search(20));
+    }
+
+    @Test
+    public void testComplexInsertDelete() {
+        BTree bTree = new BTree(2); // Smaller degree to trigger splits more easily
+        int[] values = {1, 3, 7, 10, 11, 13, 14, 15, 18, 16, 19, 24, 25, 26, 21, 4, 5, 20, 22, 2, 17, 12, 6};
+
+        for (int val : values) {
+            bTree.insert(val);
+        }
+
+        for (int val : values) {
+            assertTrue(bTree.search(val));
+        }
+
+        int[] toDelete = {6, 13, 7, 4, 2, 16};
+        for (int val : toDelete) {
+            bTree.delete(val);
+            assertFalse(bTree.search(val));
+        }
+
+        ArrayList<Integer> remaining = new ArrayList<>();
+        bTree.traverse(remaining);
+
+        for (int val : toDelete) {
+            assertFalse(remaining.contains(val));
+        }
+    }
+}