first commit

LICENSE

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+ISC License
+
+Copyright (c) 2017, Vladimir Agafonkin
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.

README.md

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+# tinyqueue
+<a href="https://godoc.org/github.com/tidwall/tinyqueue"><img src="https://img.shields.io/badge/api-reference-blue.svg?style=flat-square" alt="GoDoc"></a>
+
+tinyqueue is a Go package for binary heap priority queues.
+Ported from the [tinyqueue](https://github.com/mourner/tinyqueue) Javascript library.
+
+

tinyqueue.go

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+package tinyqueue
+
+type Queue struct {
+	length int
+	data   []Item
+}
+
+type Item interface {
+	Less(Item) bool
+}
+
+func New(data []Item) *Queue {
+	q := &Queue{}
+	q.data = data
+	q.length = len(data)
+	if q.length > 0 {
+		i := q.length >> 1
+		for ; i >= 0; i-- {
+			q.down(i)
+		}
+	}
+	return q
+}
+
+func (q *Queue) Push(item Item) {
+	q.data = append(q.data, item)
+	q.length++
+	q.up(q.length - 1)
+}
+func (q *Queue) Pop() Item {
+	if q.length == 0 {
+		return nil
+	}
+	top := q.data[0]
+	q.length--
+	if q.length > 0 {
+		q.data[0] = q.data[q.length]
+		q.down(0)
+	}
+	q.data = q.data[:len(q.data)-1]
+	return top
+}
+func (q *Queue) Peek() Item {
+	if q.length == 0 {
+		return nil
+	}
+	return q.data[0]
+}
+
+func (q *Queue) down(pos int) {
+	data := q.data
+	halfLength := q.length >> 1
+	item := data[pos]
+	for pos < halfLength {
+		left := (pos << 1) + 1
+		right := left + 1
+		best := data[left]
+		if right < q.length && data[right].Less(best) {
+			left = right
+			best = data[right]
+		}
+		if !best.Less(item) {
+			break
+		}
+		data[pos] = best
+		pos = left
+	}
+	data[pos] = item
+}
+
+func (q *Queue) up(pos int) {
+	data := q.data
+	item := data[pos]
+	for pos > 0 {
+		parent := (pos - 1) >> 1
+		current := data[parent]
+		if !item.Less(current) {
+			break
+		}
+		data[pos] = current
+		pos = parent
+	}
+	data[pos] = item
+}

tinyqueue_test.go

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+package tinyqueue
+
+import (
+	"math/rand"
+	"sort"
+	"testing"
+	"time"
+
+	"github.com/json-iterator/go/assert"
+)
+
+type floatValue float64
+
+func (a floatValue) Less(b Item) bool {
+	return a < b.(floatValue)
+}
+
+var data, sorted = func() ([]Item, []Item) {
+	rand.Seed(time.Now().UnixNano())
+	var data []Item
+	for i := 0; i < 100; i++ {
+		data = append(data, floatValue(rand.Float64()*100))
+	}
+	sorted := make([]Item, len(data))
+	copy(sorted, data)
+	sort.Slice(sorted, func(i, j int) bool {
+		return sorted[i].Less(sorted[j])
+	})
+	return data, sorted
+}()
+
+func TestMaintainsPriorityQueue(t *testing.T) {
+	q := New(nil)
+	for i := 0; i < len(data); i++ {
+		q.Push(data[i])
+	}
+	assert.Equal(t, q.Peek(), sorted[0])
+	var result []Item
+	for q.length > 0 {
+		result = append(result, q.Pop())
+	}
+	assert.Equal(t, result, sorted)
+}
+
+func TestAcceptsDataInConstructor(t *testing.T) {
+	q := New(data)
+	var result []Item
+	for q.length > 0 {
+		result = append(result, q.Pop())
+	}
+	assert.Equal(t, result, sorted)
+}
+func TestHandlesEdgeCasesWithFewElements(t *testing.T) {
+	q := New(nil)
+	q.Push(floatValue(2))
+	q.Push(floatValue(1))
+	q.Pop()
+	q.Pop()
+	q.Pop()
+	q.Push(floatValue(2))
+	q.Push(floatValue(1))
+	assert.Equal(t, float64(q.Pop().(floatValue)), 1.0)
+	assert.Equal(t, float64(q.Pop().(floatValue)), 2.0)
+	assert.Equal(t, q.Pop(), nil)
+}