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vendor/github.com/steveyen/gtreap/LICENSE

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+Copyright (C) 2012 Steve Yen
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

vendor/github.com/steveyen/gtreap/README.md

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+gtreap
+------
+
+gtreap is an immutable treap implementation in the Go Language
+
+[![GoDoc](https://godoc.org/github.com/steveyen/gtreap?status.svg)](https://godoc.org/github.com/steveyen/gtreap) [![Build Status](https://drone.io/github.com/steveyen/gtreap/status.png)](https://drone.io/github.com/steveyen/gtreap/latest) [![Coverage Status](https://coveralls.io/repos/steveyen/gtreap/badge.png)](https://coveralls.io/r/steveyen/gtreap)
+
+Overview
+========
+
+gtreap implements an immutable treap data structure in golang.
+
+By treap, this data structure is both a heap and a binary search tree.
+
+By immutable, any updates/deletes to a treap will return a new treap
+which can share internal nodes with the previous treap.  All nodes in
+this implementation are read-only after their creation.  This allows
+concurrent readers to operate safely with concurrent writers as
+modifications only create new data structures and never modify
+existing data structures.  This is a simple approach to achieving MVCC
+or multi-version concurrency control.
+
+By heap, items in the treap follow the heap-priority property, where a
+parent node will have higher priority than its left and right children
+nodes.
+
+By binary search tree, items are store lexigraphically, ordered by a
+user-supplied Compare function.
+
+To get a probabilistic O(lg N) tree height, you should use a random
+priority number during the Upsert() operation.
+
+LICENSE
+=======
+
+MIT
+
+Example
+=======
+
+    import (
+        "math/rand"
+        "github.com/steveyen/gtreap"
+    )
+    
+    func stringCompare(a, b interface{}) int {
+	    return bytes.Compare([]byte(a.(string)), []byte(b.(string)))
+    }
+    
+    t := gtreap.NewTreap(stringCompare)
+    t = t.Upsert("hi", rand.Int())
+    t = t.Upsert("hola", rand.Int())
+    t = t.Upsert("bye", rand.Int())
+    t = t.Upsert("adios", rand.Int())
+    
+    hi = t.Get("hi")
+    bye = t.Get("bye")
+    
+    // Some example Delete()'s...
+    t = t.Delete("bye")
+    nilValueHere = t.Get("bye")
+    t2 = t.Delete("hi")
+    nilValueHere2 = t2.Get("hi")
+    
+    // Since we still hold onto treap t, we can still access "hi".
+    hiStillExistsInTreapT = t.Get("hi")
+    
+    t.VisitAscend("cya", func(i Item) bool {
+        // This visitor callback will be invoked with every item
+        // from "cya" onwards.  So: "hi", "hola".
+        // If we want to stop visiting, return false;
+        // otherwise a true return result means keep visiting items.
+        return true
+    })
+
+Tips
+====
+
+The Upsert() method takes both an Item (an interface{}) and a heap
+priority.  Usually, that priority should be a random int
+(math/rand.Int()) or perhaps even a hash of the item.  However, if you
+want to shuffle more commonly accessed items nearer to the top of the
+treap for faster access, at the potential cost of not approaching a
+probabilistic O(lg N) tree height, then you might tweak the priority.
+
+See also
+========
+
+For a simple, ordered, key-value storage or persistence library built
+on immutable treaps, see: https://github.com/steveyen/gkvlite

vendor/github.com/steveyen/gtreap/treap.go

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