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package search
import "fmt"
type node struct {
key int
val int
left *node
right *node
}
func (n *node) String() string {
recurse := func(n *node) string {
if n == nil {
return ""
}
return n.String()
}
return fmt.Sprintf("node{%d:%d,%s,%s}",
n.key,
n.val,
recurse(n.left),
recurse(n.right))
}
type BST struct {
root *node
size int
}
func NewBST() *BST {
return &BST{}
}
func (t *BST) String() string {
if t.Empty() {
return "BST{}"
}
return fmt.Sprintf("BST{%s}", t.root)
}
func (t *BST) Empty() bool {
return t.root == nil
}
func (t *BST) Size() int {
return t.size
}
func (t *BST) Put(key, val int) {
if t.Empty() {
t.root = &node{key, val, nil, nil}
t.size++
return
}
ptr, _, err := t.search(&t.root, key)
switch err {
case nil:
// key already in the tree
return
case NotFound:
*ptr = &node{key, val, nil, nil}
t.size++
return
default:
panic(err)
}
}
func (t *BST) Get(key int) (int, error) {
_, n, err := t.search(&t.root, key)
if err != nil {
return 0, err
}
return n.val, nil
}
func (t *BST) Del(key int) (int, error) {
ptr, n, err := t.search(&t.root, key)
if err != nil {
return 0, err
}
t.size--
// Case 1: n is leaf node
// Case 2: n has one child
// Case 3: n has two childs
switch {
case n.left == nil:
if n.right == nil {
// I am a leaf node
*ptr = nil
return n.val, nil
}
// I have a right child
*ptr = n.right
return n.val, nil
case n.right == nil:
// I have a left child
*ptr = n.left
return n.val, nil
default:
// I have two children!
o, err := t.deleteMin(&n.right)
if err != nil {
return 0, err
}
o.left = n.left
o.right = n.right
*ptr = o
return n.val, nil
}
}
func (t *BST) search(ptr **node, key int) (**node, *node, error) {
n := *ptr
if n == nil {
return ptr, nil, NotFound
}
switch {
case key < n.key:
return t.search(&n.left, key)
case n.key < key:
return t.search(&n.right, key)
default:
return ptr, n, nil
}
}
func (t *BST) deleteMin(ptr **node) (*node, error) {
ptr, n, err := t.min(ptr)
if err != nil {
return nil, err
}
*ptr = n.right
n.right = nil
return n, nil
}
func (t *BST) min(ptr **node) (**node, *node, error) {
n := *ptr
if n == nil {
return nil, nil, NotFound
}
for {
if n.left == nil {
return ptr, n, nil
}
ptr = &n.left
n = *ptr
}
}
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