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// run
// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package orderedmap provides an ordered map, implemented as a binary tree.
package main
import (
"bytes"
"context"
"fmt"
"runtime"
)
type Ordered interface {
~int | ~int8 | ~int16 | ~int32 | ~int64 |
~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
~float32 | ~float64 |
~string
}
// _Map is an ordered map.
type _Map[K, V any] struct {
root *node[K, V]
compare func(K, K) int
}
// node is the type of a node in the binary tree.
type node[K, V any] struct {
key K
val V
left, right *node[K, V]
}
// _New returns a new map. It takes a comparison function that compares two
// keys and returns < 0 if the first is less, == 0 if they are equal,
// > 0 if the first is greater.
func _New[K, V any](compare func(K, K) int) *_Map[K, V] {
return &_Map[K, V]{compare: compare}
}
// _NewOrdered returns a new map whose key is an ordered type.
// This is like _New, but does not require providing a compare function.
// The map compare function uses the obvious key ordering.
func _NewOrdered[K Ordered, V any]() *_Map[K, V] {
return _New[K, V](func(k1, k2 K) int {
switch {
case k1 < k2:
return -1
case k1 == k2:
return 0
default:
return 1
}
})
}
// find looks up key in the map, returning either a pointer to the slot of the
// node holding key, or a pointer to the slot where should a node would go.
func (m *_Map[K, V]) find(key K) **node[K, V] {
pn := &m.root
for *pn != nil {
switch cmp := m.compare(key, (*pn).key); {
case cmp < 0:
pn = &(*pn).left
case cmp > 0:
pn = &(*pn).right
default:
return pn
}
}
return pn
}
// Insert inserts a new key/value into the map.
// If the key is already present, the value is replaced.
// Reports whether this is a new key.
func (m *_Map[K, V]) Insert(key K, val V) bool {
pn := m.find(key)
if *pn != nil {
(*pn).val = val
return false
}
*pn = &node[K, V]{key: key, val: val}
return true
}
// Find returns the value associated with a key, or the zero value
// if not present. The found result reports whether the key was found.
func (m *_Map[K, V]) Find(key K) (V, bool) {
pn := m.find(key)
if *pn == nil {
var zero V
return zero, false
}
return (*pn).val, true
}
// keyValue is a pair of key and value used while iterating.
type keyValue[K, V any] struct {
key K
val V
}
// iterate returns an iterator that traverses the map.
func (m *_Map[K, V]) Iterate() *_Iterator[K, V] {
sender, receiver := _Ranger[keyValue[K, V]]()
var f func(*node[K, V]) bool
f = func(n *node[K, V]) bool {
if n == nil {
return true
}
// Stop the traversal if Send fails, which means that
// nothing is listening to the receiver.
return f(n.left) &&
sender.Send(context.Background(), keyValue[K, V]{n.key, n.val}) &&
f(n.right)
}
go func() {
f(m.root)
sender.Close()
}()
return &_Iterator[K, V]{receiver}
}
// _Iterator is used to iterate over the map.
type _Iterator[K, V any] struct {
r *_Receiver[keyValue[K, V]]
}
// Next returns the next key and value pair, and a boolean that reports
// whether they are valid. If not valid, we have reached the end of the map.
func (it *_Iterator[K, V]) Next() (K, V, bool) {
keyval, ok := it.r.Next(context.Background())
if !ok {
var zerok K
var zerov V
return zerok, zerov, false
}
return keyval.key, keyval.val, true
}
func TestMap() {
m := _New[[]byte, int](bytes.Compare)
if _, found := m.Find([]byte("a")); found {
panic(fmt.Sprintf("unexpectedly found %q in empty map", []byte("a")))
}
if !m.Insert([]byte("a"), 'a') {
panic(fmt.Sprintf("key %q unexpectedly already present", []byte("a")))
}
if !m.Insert([]byte("c"), 'c') {
panic(fmt.Sprintf("key %q unexpectedly already present", []byte("c")))
}
if !m.Insert([]byte("b"), 'b') {
panic(fmt.Sprintf("key %q unexpectedly already present", []byte("b")))
}
if m.Insert([]byte("c"), 'x') {
panic(fmt.Sprintf("key %q unexpectedly not present", []byte("c")))
}
if v, found := m.Find([]byte("a")); !found {
panic(fmt.Sprintf("did not find %q", []byte("a")))
} else if v != 'a' {
panic(fmt.Sprintf("key %q returned wrong value %c, expected %c", []byte("a"), v, 'a'))
}
if v, found := m.Find([]byte("c")); !found {
panic(fmt.Sprintf("did not find %q", []byte("c")))
} else if v != 'x' {
panic(fmt.Sprintf("key %q returned wrong value %c, expected %c", []byte("c"), v, 'x'))
}
if _, found := m.Find([]byte("d")); found {
panic(fmt.Sprintf("unexpectedly found %q", []byte("d")))
}
gather := func(it *_Iterator[[]byte, int]) []int {
var r []int
for {
_, v, ok := it.Next()
if !ok {
return r
}
r = append(r, v)
}
}
got := gather(m.Iterate())
want := []int{'a', 'b', 'x'}
if !_SliceEqual(got, want) {
panic(fmt.Sprintf("Iterate returned %v, want %v", got, want))
}
}
func main() {
TestMap()
}
// _Equal reports whether two slices are equal: the same length and all
// elements equal. All floating point NaNs are considered equal.
func _SliceEqual[Elem comparable](s1, s2 []Elem) bool {
if len(s1) != len(s2) {
return false
}
for i, v1 := range s1 {
v2 := s2[i]
if v1 != v2 {
isNaN := func(f Elem) bool { return f != f }
if !isNaN(v1) || !isNaN(v2) {
return false
}
}
}
return true
}
// Ranger returns a Sender and a Receiver. The Receiver provides a
// Next method to retrieve values. The Sender provides a Send method
// to send values and a Close method to stop sending values. The Next
// method indicates when the Sender has been closed, and the Send
// method indicates when the Receiver has been freed.
//
// This is a convenient way to exit a goroutine sending values when
// the receiver stops reading them.
func _Ranger[Elem any]() (*_Sender[Elem], *_Receiver[Elem]) {
c := make(chan Elem)
d := make(chan struct{})
s := &_Sender[Elem]{
values: c,
done: d,
}
r := &_Receiver[Elem]{
values: c,
done: d,
}
runtime.SetFinalizer(r, (*_Receiver[Elem]).finalize)
return s, r
}
// A _Sender is used to send values to a Receiver.
type _Sender[Elem any] struct {
values chan<- Elem
done <-chan struct{}
}
// Send sends a value to the receiver. It reports whether the value was sent.
// The value will not be sent if the context is closed or the receiver
// is freed.
func (s *_Sender[Elem]) Send(ctx context.Context, v Elem) bool {
select {
case <-ctx.Done():
return false
case s.values <- v:
return true
case <-s.done:
return false
}
}
// Close tells the receiver that no more values will arrive.
// After Close is called, the _Sender may no longer be used.
func (s *_Sender[Elem]) Close() {
close(s.values)
}
// A _Receiver receives values from a _Sender.
type _Receiver[Elem any] struct {
values <-chan Elem
done chan<- struct{}
}
// Next returns the next value from the channel. The bool result indicates
// whether the value is valid.
func (r *_Receiver[Elem]) Next(ctx context.Context) (v Elem, ok bool) {
select {
case <-ctx.Done():
case v, ok = <-r.values:
}
return v, ok
}
// finalize is a finalizer for the receiver.
func (r *_Receiver[Elem]) finalize() {
close(r.done)
}