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189 lines
4.0 KiB
Go
189 lines
4.0 KiB
Go
package gtreap
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type Treap struct {
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compare Compare
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root *node
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}
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// Compare returns an integer comparing the two items
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// lexicographically. The result will be 0 if a==b, -1 if a < b, and
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// +1 if a > b.
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type Compare func(a, b interface{}) int
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// Item can be anything.
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type Item interface{}
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type node struct {
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item Item
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priority int
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left *node
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right *node
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}
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func NewTreap(c Compare) *Treap {
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return &Treap{compare: c, root: nil}
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}
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func (t *Treap) Min() Item {
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n := t.root
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if n == nil {
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return nil
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}
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for n.left != nil {
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n = n.left
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}
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return n.item
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}
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func (t *Treap) Max() Item {
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n := t.root
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if n == nil {
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return nil
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}
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for n.right != nil {
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n = n.right
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}
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return n.item
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}
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func (t *Treap) Get(target Item) Item {
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n := t.root
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for n != nil {
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c := t.compare(target, n.item)
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if c < 0 {
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n = n.left
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} else if c > 0 {
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n = n.right
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} else {
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return n.item
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}
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}
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return nil
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}
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// Note: only the priority of the first insert of an item is used.
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// Priorities from future updates on already existing items are
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// ignored. To change the priority for an item, you need to do a
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// Delete then an Upsert.
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func (t *Treap) Upsert(item Item, itemPriority int) *Treap {
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r := t.union(t.root, &node{item: item, priority: itemPriority})
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return &Treap{compare: t.compare, root: r}
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}
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func (t *Treap) union(this *node, that *node) *node {
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if this == nil {
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return that
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}
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if that == nil {
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return this
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}
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if this.priority > that.priority {
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left, middle, right := t.split(that, this.item)
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if middle == nil {
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return &node{
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item: this.item,
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priority: this.priority,
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left: t.union(this.left, left),
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right: t.union(this.right, right),
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}
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}
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return &node{
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item: middle.item,
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priority: this.priority,
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left: t.union(this.left, left),
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right: t.union(this.right, right),
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}
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}
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// We don't use middle because the "that" has precendence.
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left, _, right := t.split(this, that.item)
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return &node{
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item: that.item,
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priority: that.priority,
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left: t.union(left, that.left),
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right: t.union(right, that.right),
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}
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}
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// Splits a treap into two treaps based on a split item "s".
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// The result tuple-3 means (left, X, right), where X is either...
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// nil - meaning the item s was not in the original treap.
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// non-nil - returning the node that had item s.
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// The tuple-3's left result treap has items < s,
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// and the tuple-3's right result treap has items > s.
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func (t *Treap) split(n *node, s Item) (*node, *node, *node) {
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if n == nil {
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return nil, nil, nil
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}
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c := t.compare(s, n.item)
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if c == 0 {
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return n.left, n, n.right
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}
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if c < 0 {
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left, middle, right := t.split(n.left, s)
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return left, middle, &node{
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item: n.item,
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priority: n.priority,
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left: right,
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right: n.right,
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}
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}
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left, middle, right := t.split(n.right, s)
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return &node{
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item: n.item,
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priority: n.priority,
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left: n.left,
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right: left,
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}, middle, right
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}
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func (t *Treap) Delete(target Item) *Treap {
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left, _, right := t.split(t.root, target)
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return &Treap{compare: t.compare, root: t.join(left, right)}
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}
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// All the items from this are < items from that.
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func (t *Treap) join(this *node, that *node) *node {
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if this == nil {
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return that
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}
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if that == nil {
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return this
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}
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if this.priority > that.priority {
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return &node{
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item: this.item,
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priority: this.priority,
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left: this.left,
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right: t.join(this.right, that),
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}
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}
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return &node{
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item: that.item,
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priority: that.priority,
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left: t.join(this, that.left),
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right: that.right,
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}
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}
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type ItemVisitor func(i Item) bool
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// Visit items greater-than-or-equal to the pivot.
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func (t *Treap) VisitAscend(pivot Item, visitor ItemVisitor) {
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t.visitAscend(t.root, pivot, visitor)
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}
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func (t *Treap) visitAscend(n *node, pivot Item, visitor ItemVisitor) bool {
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if n == nil {
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return true
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}
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if t.compare(pivot, n.item) <= 0 {
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if !t.visitAscend(n.left, pivot, visitor) {
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return false
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}
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if !visitor(n.item) {
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return false
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}
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}
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return t.visitAscend(n.right, pivot, visitor)
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}
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