- btree don't allow order less than 3

- btree Left(), Right(), LeftKey(), RightKey(), LeftValue(), RightValue() implementation with tests

trees/btree/btree.go

@@ -44,8 +44,8 @@ type Entry struct {
 
 // NewWith instantiates a B-tree with the order (maximum number of children) and a custom key comparator.
 func NewWith(order int, comparator utils.Comparator) *Tree {
-	if order < 2 {
-		panic("Invalid order, should be at least 2")
+	if order < 3 {
+		panic("Invalid order, should be at least 3")
 	}
 	return &Tree{m: order, Comparator: comparator}
 }
@@ -134,6 +134,66 @@ func (tree *Tree) Height() int {
 	return tree.Root.height()
 }
 
+// Left returns the left-most (min) node or nil if tree is empty.
+func (tree *Tree) Left() *Node {
+	if tree.Empty() {
+		return nil
+	}
+	node := tree.Root
+	for {
+		if tree.isLeaf(node) {
+			return node
+		}
+		node = node.Children[0]
+	}
+}
+
+// LeftKey returns the left-most (min) key or nil if tree is empty.
+func (tree *Tree) LeftKey() interface{} {
+	if left := tree.Left(); left != nil {
+		return left.Entries[0].Key
+	}
+	return nil
+}
+
+// LeftValue returns the left-most value or nil if tree is empty.
+func (tree *Tree) LeftValue() interface{} {
+	if left := tree.Left(); left != nil {
+		return left.Entries[0].Value
+	}
+	return nil
+}
+
+// Right returns the right-most (max) node or nil if tree is empty.
+func (tree *Tree) Right() *Node {
+	if tree.Empty() {
+		return nil
+	}
+	node := tree.Root
+	for {
+		if tree.isLeaf(node) {
+			return node
+		}
+		node = node.Children[len(node.Children)-1]
+	}
+}
+
+// RightKey returns the right-most (max) key or nil if tree is empty.
+func (tree *Tree) RightKey() interface{} {
+	if right := tree.Right(); right != nil {
+		return right.Entries[len(right.Entries)-1].Key
+	}
+	return nil
+}
+
+// RightValue returns the right-most value or nil if tree is empty.
+func (tree *Tree) RightValue() interface{} {
+	if right := tree.Right(); right != nil {
+		return right.Entries[len(right.Entries)-1].Value
+	}
+	return nil
+}
+
 // String returns a string representation of container (for debugging purposes)
 func (tree *Tree) String() string {
 	var buffer bytes.Buffer

trees/btree/btree_test.go

@@ -350,6 +350,40 @@ func TestBTreeHeight(t *testing.T) {
 	}
 }
 
+func TestBTreeLeftAndRight(t *testing.T) {
+	tree := NewWithIntComparator(3)
+
+	if actualValue := tree.Left(); actualValue != nil {
+		t.Errorf("Got %v expected %v", actualValue, nil)
+	}
+	if actualValue := tree.Right(); actualValue != nil {
+		t.Errorf("Got %v expected %v", actualValue, nil)
+	}
+
+	tree.Put(1, "a")
+	tree.Put(5, "e")
+	tree.Put(6, "f")
+	tree.Put(7, "g")
+	tree.Put(3, "c")
+	tree.Put(4, "d")
+	tree.Put(1, "x") // overwrite
+	tree.Put(2, "b")
+
+	if actualValue, expectedValue := tree.LeftKey(), 1; actualValue != expectedValue {
+		t.Errorf("Got %v expected %v", actualValue, expectedValue)
+	}
+	if actualValue, expectedValue := tree.LeftValue(), "x"; actualValue != expectedValue {
+		t.Errorf("Got %v expected %v", actualValue, expectedValue)
+	}
+
+	if actualValue, expectedValue := tree.RightKey(), 7; actualValue != expectedValue {
+		t.Errorf("Got %v expected %v", actualValue, expectedValue)
+	}
+	if actualValue, expectedValue := tree.RightValue(), "g"; actualValue != expectedValue {
+		t.Errorf("Got %v expected %v", actualValue, expectedValue)
+	}
+}
+
 func TestBTree_search(t *testing.T) {
 	{
 		tree := NewWithIntComparator(3)