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forgejo/vendor/github.com/petar/GoLLRB/llrb/llrb.go

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// Copyright 2010 Petar Maymounkov. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// A Left-Leaning Red-Black (LLRB) implementation of 2-3 balanced binary search trees,
// based on the following work:
//
// http://www.cs.princeton.edu/~rs/talks/LLRB/08Penn.pdf
// http://www.cs.princeton.edu/~rs/talks/LLRB/LLRB.pdf
// http://www.cs.princeton.edu/~rs/talks/LLRB/Java/RedBlackBST.java
//
// 2-3 trees (and the run-time equivalent 2-3-4 trees) are the de facto standard BST
// algoritms found in implementations of Python, Java, and other libraries. The LLRB
// implementation of 2-3 trees is a recent improvement on the traditional implementation,
// observed and documented by Robert Sedgewick.
//
package llrb
// Tree is a Left-Leaning Red-Black (LLRB) implementation of 2-3 trees
type LLRB struct {
count int
root *Node
}
type Node struct {
Item
Left, Right *Node // Pointers to left and right child nodes
Black bool // If set, the color of the link (incoming from the parent) is black
// In the LLRB, new nodes are always red, hence the zero-value for node
}
type Item interface {
Less(than Item) bool
}
//
func less(x, y Item) bool {
if x == pinf {
return false
}
if x == ninf {
return true
}
return x.Less(y)
}
// Inf returns an Item that is "bigger than" any other item, if sign is positive.
// Otherwise it returns an Item that is "smaller than" any other item.
func Inf(sign int) Item {
if sign == 0 {
panic("sign")
}
if sign > 0 {
return pinf
}
return ninf
}
var (
ninf = nInf{}
pinf = pInf{}
)
type nInf struct{}
func (nInf) Less(Item) bool {
return true
}
type pInf struct{}
func (pInf) Less(Item) bool {
return false
}
// New() allocates a new tree
func New() *LLRB {
return &LLRB{}
}
// SetRoot sets the root node of the tree.
// It is intended to be used by functions that deserialize the tree.
func (t *LLRB) SetRoot(r *Node) {
t.root = r
}
// Root returns the root node of the tree.
// It is intended to be used by functions that serialize the tree.
func (t *LLRB) Root() *Node {
return t.root
}
// Len returns the number of nodes in the tree.
func (t *LLRB) Len() int { return t.count }
// Has returns true if the tree contains an element whose order is the same as that of key.
func (t *LLRB) Has(key Item) bool {
return t.Get(key) != nil
}
// Get retrieves an element from the tree whose order is the same as that of key.
func (t *LLRB) Get(key Item) Item {
h := t.root
for h != nil {
switch {
case less(key, h.Item):
h = h.Left
case less(h.Item, key):
h = h.Right
default:
return h.Item
}
}
return nil
}
// Min returns the minimum element in the tree.
func (t *LLRB) Min() Item {
h := t.root
if h == nil {
return nil
}
for h.Left != nil {
h = h.Left
}
return h.Item
}
// Max returns the maximum element in the tree.
func (t *LLRB) Max() Item {
h := t.root
if h == nil {
return nil
}
for h.Right != nil {
h = h.Right
}
return h.Item
}
func (t *LLRB) ReplaceOrInsertBulk(items ...Item) {
for _, i := range items {
t.ReplaceOrInsert(i)
}
}
func (t *LLRB) InsertNoReplaceBulk(items ...Item) {
for _, i := range items {
t.InsertNoReplace(i)
}
}
// ReplaceOrInsert inserts item into the tree. If an existing
// element has the same order, it is removed from the tree and returned.
func (t *LLRB) ReplaceOrInsert(item Item) Item {
if item == nil {
panic("inserting nil item")
}
var replaced Item
t.root, replaced = t.replaceOrInsert(t.root, item)
t.root.Black = true
if replaced == nil {
t.count++
}
return replaced
}
func (t *LLRB) replaceOrInsert(h *Node, item Item) (*Node, Item) {
if h == nil {
return newNode(item), nil
}
h = walkDownRot23(h)
var replaced Item
if less(item, h.Item) { // BUG
h.Left, replaced = t.replaceOrInsert(h.Left, item)
} else if less(h.Item, item) {
h.Right, replaced = t.replaceOrInsert(h.Right, item)
} else {
replaced, h.Item = h.Item, item
}
h = walkUpRot23(h)
return h, replaced
}
// InsertNoReplace inserts item into the tree. If an existing
// element has the same order, both elements remain in the tree.
func (t *LLRB) InsertNoReplace(item Item) {
if item == nil {
panic("inserting nil item")
}
t.root = t.insertNoReplace(t.root, item)
t.root.Black = true
t.count++
}
func (t *LLRB) insertNoReplace(h *Node, item Item) *Node {
if h == nil {
return newNode(item)
}
h = walkDownRot23(h)
if less(item, h.Item) {
h.Left = t.insertNoReplace(h.Left, item)
} else {
h.Right = t.insertNoReplace(h.Right, item)
}
return walkUpRot23(h)
}
// Rotation driver routines for 2-3 algorithm
func walkDownRot23(h *Node) *Node { return h }
func walkUpRot23(h *Node) *Node {
if isRed(h.Right) && !isRed(h.Left) {
h = rotateLeft(h)
}
if isRed(h.Left) && isRed(h.Left.Left) {
h = rotateRight(h)
}
if isRed(h.Left) && isRed(h.Right) {
flip(h)
}
return h
}
// Rotation driver routines for 2-3-4 algorithm
func walkDownRot234(h *Node) *Node {
if isRed(h.Left) && isRed(h.Right) {
flip(h)
}
return h
}
func walkUpRot234(h *Node) *Node {
if isRed(h.Right) && !isRed(h.Left) {
h = rotateLeft(h)
}
if isRed(h.Left) && isRed(h.Left.Left) {
h = rotateRight(h)
}
return h
}
// DeleteMin deletes the minimum element in the tree and returns the
// deleted item or nil otherwise.
func (t *LLRB) DeleteMin() Item {
var deleted Item
t.root, deleted = deleteMin(t.root)
if t.root != nil {
t.root.Black = true
}
if deleted != nil {
t.count--
}
return deleted
}
// deleteMin code for LLRB 2-3 trees
func deleteMin(h *Node) (*Node, Item) {
if h == nil {
return nil, nil
}
if h.Left == nil {
return nil, h.Item
}
if !isRed(h.Left) && !isRed(h.Left.Left) {
h = moveRedLeft(h)
}
var deleted Item
h.Left, deleted = deleteMin(h.Left)
return fixUp(h), deleted
}
// DeleteMax deletes the maximum element in the tree and returns
// the deleted item or nil otherwise
func (t *LLRB) DeleteMax() Item {
var deleted Item
t.root, deleted = deleteMax(t.root)
if t.root != nil {
t.root.Black = true
}
if deleted != nil {
t.count--
}
return deleted
}
func deleteMax(h *Node) (*Node, Item) {
if h == nil {
return nil, nil
}
if isRed(h.Left) {
h = rotateRight(h)
}
if h.Right == nil {
return nil, h.Item
}
if !isRed(h.Right) && !isRed(h.Right.Left) {
h = moveRedRight(h)
}
var deleted Item
h.Right, deleted = deleteMax(h.Right)
return fixUp(h), deleted
}
// Delete deletes an item from the tree whose key equals key.
// The deleted item is return, otherwise nil is returned.
func (t *LLRB) Delete(key Item) Item {
var deleted Item
t.root, deleted = t.delete(t.root, key)
if t.root != nil {
t.root.Black = true
}
if deleted != nil {
t.count--
}
return deleted
}
func (t *LLRB) delete(h *Node, item Item) (*Node, Item) {
var deleted Item
if h == nil {
return nil, nil
}
if less(item, h.Item) {
if h.Left == nil { // item not present. Nothing to delete
return h, nil
}
if !isRed(h.Left) && !isRed(h.Left.Left) {
h = moveRedLeft(h)
}
h.Left, deleted = t.delete(h.Left, item)
} else {
if isRed(h.Left) {
h = rotateRight(h)
}
// If @item equals @h.Item and no right children at @h
if !less(h.Item, item) && h.Right == nil {
return nil, h.Item
}
// PETAR: Added 'h.Right != nil' below
if h.Right != nil && !isRed(h.Right) && !isRed(h.Right.Left) {
h = moveRedRight(h)
}
// If @item equals @h.Item, and (from above) 'h.Right != nil'
if !less(h.Item, item) {
var subDeleted Item
h.Right, subDeleted = deleteMin(h.Right)
if subDeleted == nil {
panic("logic")
}
deleted, h.Item = h.Item, subDeleted
} else { // Else, @item is bigger than @h.Item
h.Right, deleted = t.delete(h.Right, item)
}
}
return fixUp(h), deleted
}
// Internal node manipulation routines
func newNode(item Item) *Node { return &Node{Item: item} }
func isRed(h *Node) bool {
if h == nil {
return false
}
return !h.Black
}
func rotateLeft(h *Node) *Node {
x := h.Right
if x.Black {
panic("rotating a black link")
}
h.Right = x.Left
x.Left = h
x.Black = h.Black
h.Black = false
return x
}
func rotateRight(h *Node) *Node {
x := h.Left
if x.Black {
panic("rotating a black link")
}
h.Left = x.Right
x.Right = h
x.Black = h.Black
h.Black = false
return x
}
// REQUIRE: Left and Right children must be present
func flip(h *Node) {
h.Black = !h.Black
h.Left.Black = !h.Left.Black
h.Right.Black = !h.Right.Black
}
// REQUIRE: Left and Right children must be present
func moveRedLeft(h *Node) *Node {
flip(h)
if isRed(h.Right.Left) {
h.Right = rotateRight(h.Right)
h = rotateLeft(h)
flip(h)
}
return h
}
// REQUIRE: Left and Right children must be present
func moveRedRight(h *Node) *Node {
flip(h)
if isRed(h.Left.Left) {
h = rotateRight(h)
flip(h)
}
return h
}
func fixUp(h *Node) *Node {
if isRed(h.Right) {
h = rotateLeft(h)
}
if isRed(h.Left) && isRed(h.Left.Left) {
h = rotateRight(h)
}
if isRed(h.Left) && isRed(h.Right) {
flip(h)
}
return h
}