mirror of
https://github.com/go-gitea/gitea
synced 2024-11-15 22:54:24 +00:00
91 lines
3.0 KiB
Markdown
91 lines
3.0 KiB
Markdown
|
gtreap
|
||
|
|
------
|
||
|
|
|
||
|
|
gtreap is an immutable treap implementation in the Go Language
|
||
|
|
|
||
|
|
[](https://godoc.org/github.com/steveyen/gtreap) [](https://drone.io/github.com/steveyen/gtreap/latest) [](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
|