new file: trees/avl/AvlTree.go

README.md

@@ -11,7 +11,7 @@
 ## Tree — hierarchical, parent/child relationships
 
 - [x] Binary Search Tree
-- [ ] AVL Tree
+- [x] AVL Tree
 - [ ] Heap (min/max)
 - [ ] Trie
 

trees/avl/AvlTree.go

@@ -0,0 +1,134 @@
+package avl
+
+type numericTypes interface {
+	int | int8 | int16 | int32 | int64 |
+		uint | uint8 | uint16 | uint32 | uint64 |
+		float32 | float64
+}
+
+type AvlNode[T numericTypes] struct {
+	Left   *AvlNode[T]
+	Right  *AvlNode[T]
+	Data   T
+	Height int
+}
+
+type AvlTree[T numericTypes] struct {
+	Root *AvlNode[T]
+}
+
+// NewAvlTree() -> creates an AVL tree
+func NewAvlTree[T numericTypes]() *AvlTree[T] {
+	return &AvlTree[T]{}
+}
+
+// height() ->  0 if root
+func height[T numericTypes](n *AvlNode[T]) int {
+	if n == nil {
+		return 0
+	}
+	return n.Height
+}
+
+// updateHeight()
+func updateHeight[T numericTypes](node *AvlNode[T]) {
+	node.Height = 1 + max(height(node.Left), height(node.Right))
+}
+
+// balanceFactor() -> only 0 , -1 ,-2 ok
+func balanceFactor[T numericTypes](n *AvlNode[T]) int {
+	if n == nil {
+		return 0
+	}
+
+	return height(n.Left) - height(n.Right)
+}
+
+// rotateRight() -> fixes a left heavy subtree, returns the new subtree root
+func rotateRight[T numericTypes](y *AvlNode[T]) *AvlNode[T] {
+	x := y.Left
+	b := x.Right
+
+	x.Right = y
+	y.Left = b
+
+	updateHeight(y)
+	updateHeight(x)
+
+	return x
+}
+
+// rotateLeft() -> fixes a right heavy subtree, returns the new subtree root
+func rotateLeft[T numericTypes](x *AvlNode[T]) *AvlNode[T] {
+	y := x.Right
+	b := y.Left
+
+	y.Left = x
+	x.Right = b
+
+	updateHeight(x)
+	updateHeight(y)
+
+	return y
+}
+
+// Insert() -> inserts data, keeping the tree balanced
+func (tree *AvlTree[T]) Insert(data T) {
+	tree.Root = insertHelper(tree.Root, data)
+}
+
+func insertHelper[T numericTypes](node *AvlNode[T], data T) *AvlNode[T] {
+	//  normal BST insert
+	if node == nil {
+		return &AvlNode[T]{Data: data, Height: 1}
+	}
+
+	if data < node.Data {
+		node.Left = insertHelper(node.Left, data)
+	} else if data > node.Data {
+		node.Right = insertHelper(node.Right, data)
+	} else {
+		return node // duplicate, ignore
+	}
+
+	updateHeight(node)
+
+	bf := balanceFactor(node)
+
+	if bf > 1 {
+		if data > node.Left.Data { // Left-Right case
+			node.Left = rotateLeft(node.Left)
+		}
+		return rotateRight(node) // Left-Left case
+	}
+
+	if bf < -1 {
+		if data < node.Right.Data {
+			node.Right = rotateRight(node.Right)
+		}
+		return rotateLeft(node)
+	}
+
+	return node
+}
+
+// Find() => binary search implementation returns a pointer to the node and true if val is found in tree, else returns zero struct and false
+func (t AvlTree[T]) Find(val T) (*AvlNode[T], bool) {
+	zero := &AvlNode[T]{}
+
+	if t.Root == nil {
+		return zero, false
+	}
+
+	for t.Root != nil {
+		if val == t.Root.Data {
+			return t.Root, true
+		} else if val < t.Root.Data {
+			t.Root = t.Root.Left
+		} else if val > t.Root.Data {
+			t.Root = t.Root.Right
+		}
+	}
+
+	return zero, false
+}