// PreOrder returns an iterator over the tree depth-first in
// preorder:
// Traverse the left subtree.
// Visit the root.
// Traverse the right subtree.
//
// e.g. for x := range (2 (1) (3)).PreOrder() { x } => 2, 1, 3
//
func (T *BinaryTree) PreOrder() chan Elem {
ch := make(chan Elem, T.size)
go func() {
if T.Empty() {
close(ch)
return
}
nodes := stack.New()
nodes.Push(T.root)
for !nodes.Empty() {
currentNode := nodes.Pop().(*node)
ch <- currentNode.elem
if currentNode.right != nil {
nodes.Push(currentNode.right)
}
if currentNode.left != nil {
nodes.Push(currentNode.left)
}
}
close(ch)
}()
return ch
}
// InOrder returns an iterator over the tree depth-first inorder:
// Visit the root.
// Traverse the left subtree.
// Traverse the right subtree.
//
// e.g. for x := range (2 (1) (3)).InOrder() { x } => 1, 2, 3
//
func (T *BinaryTree) InOrder() chan Elem {
ch := make(chan Elem, T.size)
go func() {
nodes := stack.New()
currentNode := T.root
for {
if currentNode != nil {
nodes.Push(currentNode)
currentNode = currentNode.left
} else {
if !nodes.Empty() {
currentNode = nodes.Pop().(*node)
ch <- currentNode.elem
currentNode = currentNode.right
} else {
break
}
}
}
close(ch)
}()
return ch
}
// PostOrder returns an iterator over the tree depth-first in
// postorder:
// Traverse the left subtree.
// Traverse the right subtree.
// Visit the root.
//
// e.g. for x := range (2 (1) (3)).PostOrder() { x } => 1, 3, 2
//
func (T *BinaryTree) PostOrder() chan Elem {
ch := make(chan Elem, T.size)
go func() {
if T.Empty() {
close(ch)
return
}
nodes := stack.New()
nodes.Push(T.root)
var prev *node
for !nodes.Empty() {
current := nodes.Peek().(*node)
if prev == nil || prev.left == current || prev.right == current {
if current.left != nil {
nodes.Push(current.left)
} else if current.right != nil {
nodes.Push(current.right)
}
} else if current.left == prev {
if current.right != nil {
nodes.Push(current.right)
}
} else {
ch <- current.elem
nodes.Pop()
}
prev = current
}
close(ch)
}()
return ch
}
