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golang基本数据结构与算法之如何使用哈希表
这篇文章主要讲解了“golang基本数据结构与算法之如何使用哈希表”，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习“golang基本数据结构与算法之如何使用哈希表”吧！
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哈希表
哈希表存储的是由键（key）和值（value）组成的数据。 在哈希表中，我们可以利用哈希函数快速访问到数组中的目标数据。 如果发生哈希冲突(哈希函数对不同的键, 返回了相同的哈希值)， 就使用链表进行存储(因此, 哈希表一般至少是数组+链表的二维结构)。 如果数组的空间太小， 使用哈希表的时候就容易发生冲突， 线性查找的使用频率也会更高； 反过来，如果数组的空间太大， 就会出现很多空箱子，造成内存的浪费。 摘自 <<我的第一本算法书>>(【日】石田保辉；宫崎修一)
目标
实现一个哈希表, 提供对键值对数据的增删改查, 且性能不能太差
物理结构
采用分区 + 数组 + 链表的三维结构
分区是一个双向链表, 由小到大呈2次幂增长
当前分区总是指向最新也是最大的那个分区
查找某个键时, 需要遍历所有分区
哈希函数
合适的哈希函数对性能影响非常巨大
对哈希函数的要求一般是足够快, 足够"散", 对不同键值最好能随机均匀分布
本示例采用hash/crc64, 多项式为ECMA
如果哈希函数的计算比较耗时, 则应当尽可能重复利用计算结果
扩容与缩容
填充因子为3/4, 即当前分区的元素数>容量的3/4时, 创建2倍大的新分区
扩容不做任何拷贝和rehash.
扩容后, 非当前分区变成只读和只删.
扩容
缩容: 当某个分区未持有任何元素, 且不为当前分区时, 删除此分区
设计
IHasher: 哈希支持接口, 定义哈希计算函数, 和键值相等比较函数
IMap: 哈希表接口
IMapIterator: 哈希表迭代器接口
tCrc64Hasher:
基于hash/crc64, 实现IHasher接口.
支持多种键类型
对于整型的键, 返回自身;
其他类型的键, 转为%v字符串再计算crc64的哈希值.
tHashMap: 哈希表的实现, 使用分区(双链)+数组+链表(单链)三维结构
tPartition: 哈希表分区. 其大小呈2次幂
tBucket: 哈希桶, 每个桶内的任何元素, 哈希值是一致的
tHashMapIterator: 哈希表迭代器的实现
单元测试
hashmap_test.go, 除基本功能测试, 还测试了百万键值插入+遍历的性能
package data_structure
import (
"fmt"
"learning/gooop/data_structure/hashmap"
"strconv"
"testing"
"time"
)
func Test_HashMap(t *testing.T) {
fnAssertTrue := func(b bool, msg string) {
if !b {
t.Fatal(msg)
}
}
fnEquals := func(a interface{}, b interface{}) bool {
i1,b1 := a.(int)
if b1 {
i2,b2 := b.(int)
if b2 {
return i1 == i2
}
}
s1,b1 := a.(string)
if b1 {
s2,b2 := b.(string)
if b2 {
return s1 == s2
}
}
return a == b
}
hasher := hashmap.NewCrc64Hashful(fnEquals)
hm := hashmap.NewHashMap(hasher, 2)
hm.Put(1, "10")
t.Log(hm)
fnAssertTrue(hm.Size() == 1, "expecting size == 1")
fnAssertTrue(hm.IsNotEmpty(), "expecting not empty")
ok,v := hm.Get(1)
fnAssertTrue(ok, "expecting ok")
fnAssertTrue(v == "10", "expecting 10")
hm.Put(2, "20")
hm.Put(3, "30")
hm.Put(4, "40")
hm.Put(5, "50")
t.Log(hm)
fnAssertTrue(hm.Size() == 5, "expecting size == 5")
ok,v = hm.Get(2)
fnAssertTrue(ok == true && v == "20", "expecting true and 20")
hm.Clear()
t.Log(hm)
fnAssertTrue(hm.Size() == 0, "expecting size == 0")
fnAssertTrue(hm.IsEmpty(), "expecting empty")
iter := hm.Iterator()
fnAssertTrue(!iter.More(), "expecting no more")
hm.Put(1, "10")
hm.Put(2, "20")
hm.Put(3, "30")
t.Log(hm)
fnAssertTrue(hm.Has(1) && hm.Has(2) && hm.Has(3) && !hm.Has(4), "expecting has 1,2,3")
hm.Put(4, "40")
hm.Put(5, "50")
hm.Put(6, "60")
t.Log(hm)
iter = hm.Iterator()
fnAssertTrue(iter.More(), "expecting more")
e,k,v := iter.Next()
t.Logf("%v>%s", k, v)
fnAssertTrue(e == nil, "e == nil")
e,k,v = iter.Next()
t.Logf("%v>%s", k, v)
fnAssertTrue(e == nil, "e == nil")
e,k,v = iter.Next()
t.Logf("%v>%s", k, v)
fnAssertTrue(e == nil, "e == nil")
e,k,v = iter.Next()
t.Logf("%v>%s", k, v)
fnAssertTrue(e == nil, "e == nil")
e,k,v = iter.Next()
t.Logf("%v>%s", k, v)
fnAssertTrue(e == nil, "e == nil")
e,k,v = iter.Next()
t.Logf("%v>%s", k, v)
fnAssertTrue(e == nil, "e == nil")
e,k,v = iter.Next()
fnAssertTrue(e != nil, "expecting e != nil")
ok,v = hm.Remove(3)
t.Log(hm)
fnAssertTrue(ok && v == "30" && hm.Size() == 5, "expecting remove 30")
ok,v = hm.Remove(2)
t.Log(hm)
fnAssertTrue(ok && v == "20" && hm.Size() == 4, "expecting remove 20")
t0 := time.Now().UnixNano()
hm.Clear()
size := 1000 * 1000
for i := 0; i < size;i++ {
hm.Put(strconv.Itoa(i), i)
}
millis := (time.Now().UnixNano() - t0) / 1000000
t.Logf("putting %v string>int = %v ms", size, millis)
fnAssertTrue(hm.Size() == size, fmt.Sprintf("expecting %v", size))
for i := 0;i < size;i++ {
ok, v = hm.Get(strconv.Itoa(i))
fnAssertTrue(ok == true && v == i, "expecting i")
}
}测试输出
$ go test -v hashmap_test.go === RUN Test_HashMap hashmap_test.go:42: s=1,v=1 p[1:b[1 1]] hashmap_test.go:54: s=5,v=5 p[4:b[1 4],5:b[1 5]] p[1:b[1 1],2:b[1 2],3:b[1 3]] hashmap_test.go:60: s=0,v=6 p[] hashmap_test.go:70: s=3,v=9 p[1:b[1 1],2:b[1 2],3:b[1 3]] hashmap_test.go:76: s=6,v=12 p[1:b[1 1],2:b[1 2],3:b[1 3],4:b[1 4],5:b[1 5],6:b[1 6]] hashmap_test.go:80: 1>10 hashmap_test.go:83: 2>20 hashmap_test.go:86: 3>30 hashmap_test.go:89: 4>40 hashmap_test.go:92: 5>50 hashmap_test.go:95: 6>60 hashmap_test.go:101: s=5,v=13 p[1:b[1 1],2:b[1 2],4:b[1 4],5:b[1 5],6:b[1 6]] hashmap_test.go:105: s=4,v=14 p[1:b[1 1],4:b[1 4],5:b[1 5],6:b[1 6]] hashmap_test.go:115: putting 1000000 string>int = 1590 ms --- PASS: Test_HashMap (2.17s) PASS ok command-line-arguments 2.181s
IHasher.go
哈希支持接口, 定义哈希计算函数, 和键值相等比较函数
package hashmap
type IHasher interface {
Hash(key interface{}) uint64
Equals(a interface{}, b interface{}) bool
}IMap.go
哈希表接口
package hashmap
type IMap interface {
Size() int
IsEmpty() bool
IsNotEmpty() bool
Put(key interface{}, value interface{})
Get(key interface{}) (bool,interface{})
Has(key interface{}) bool
Remove(key interface{}) (bool, interface{})
Clear()
Iterator() IMapIterator
String() string
}IMapIterator.go
哈希表迭代器接口
package hashmap
type IMapIterator interface {
More() bool
Next() (err error, key interface{}, value interface{})
}tCrc64Hasher.go
基于hash/crc64, 实现IHasher接口.
支持多种键类型
对于整型的键, 返回自身;
其他类型的键, 转为%v字符串再计算crc64的哈希值.
package hashmap
import (
"fmt"
"hash/crc64"
)
var gCrc64Table = crc64.MakeTable(crc64.ECMA)
type FnEquals func(a interface{}, b interface{}) bool
type tCrc64Hasher struct {
fnEquals FnEquals
}
const INT_MAX = int(^uint(0) >> 1)
const INT_MIN = ^INT_MAX
const INT32_MAX = int32(^uint32(0) >> 1)
const INT32_MIN = ^INT32_MAX
const INT64_MAX = int64(^uint64(0) >> 1)
const INT64_MIN = ^INT64_MAX
func (me *tCrc64Hasher) Hash(it interface{}) uint64 {
if it == nil {
return 0
}
if v,ok := it.(int);ok {
return uint64(v - INT_MIN)
} else if v,ok := it.(int64);ok {
return uint64(v - INT64_MIN)
} else if v,ok := it.(int32);ok {
return uint64(v - INT32_MIN)
} else if v,ok := it.(uint32);ok {
return uint64(v)
} else if v,ok := it.(uint64);ok {
return v
} else if v,ok := it.(string);ok {
return crc64.Checksum([]byte(v), gCrc64Table)
} else {
data := []byte(fmt.Sprintf("%v", it))
return crc64.Checksum(data, gCrc64Table)
}
}
func (me *tCrc64Hasher) Equals(a interface{}, b interface{}) bool {
if a == nil && b == nil {
return true
}
if a == nil || b == nil {
return false
}
fn := me.fnEquals
if fn == nil {
return a == b
} else {
return fn(a, b)
}
}
func NewCrc64Hashful(fn FnEquals) IHasher {
return &tCrc64Hasher{
fnEquals: fn,
}
}tHashMap.go
哈希表的实现, 使用分区(双链)+数组+链表(单链)三维结构
package hashmap
import (
"fmt"
"strings"
)
type tHashMap struct {
hasher IHasher
partitions *tPartition
size int
version int
}
func NewHashMap(hasher IHasher, capacity int) IMap {
if capacity < 4 {
capacity = 4
}
part := newPartition(hasher, capacity)
return &tHashMap{
hasher: hasher,
partitions: part,
size: 0,
version: 0,
}
}
func (me *tHashMap) Size() int {
return me.size
}
func (me *tHashMap) IsEmpty() bool {
return me.Size() <= 0
}
func (me *tHashMap) IsNotEmpty() bool {
return !me.IsEmpty()
}
func (me *tHashMap) Put(key interface{}, value interface{}) {
hash := me.hasher.Hash(key)
ok, _, bucket, node, _ := me.findByKeyAndHash(key, hash)
if ok {
bucket.putAt(node, key, value)
} else {
if me.partitions.nearlyFull() {
// create new partition
part := newPartition(me.hasher, int(me.partitions.bucketCount * 2))
part.next = me.partitions
me.partitions.prev = part
me.partitions = part
part.appendByKeyAndHash(key, value, hash)
} else {
me.partitions.appendByKeyAndHash(key, value, hash)
}
me.size++
}
me.version++
}
func (me *tHashMap) findByKey(key interface{}) (ok bool, part *tPartition, bucket *tBucket, node *tLinkedNode, prev *tLinkedNode) {
hash := me.hasher.Hash(key)
return me.findByKeyAndHash(key, hash)
}
func (me *tHashMap) findByKeyAndHash(key interface{}, hash uint64) (ok bool, part *tPartition, bucket *tBucket, node *tLinkedNode, prev *tLinkedNode) {
for part = me.partitions; part != nil; part = part.next {
ok, bucket, node, prev = part.findByKeyAndHash(key, hash)
if ok {
return ok, part, bucket, node, prev
}
}
return false, nil, nil, nil, nil
}
func (me *tHashMap) Get(key interface{}) (bool,interface{}) {
ok, _, _, node, _ := me.findByKey(key)
if ok {
return true, node.value
} else {
return false, nil
}
}
func (me *tHashMap) Has(key interface{}) bool {
ok, _, _, _, _ := me.findByKey(key)
return ok
}
func (me *tHashMap) Remove(key interface{}) (ok bool, value interface{}) {
ok, part, bucket, node, prev := me.findByKey(key)
if ok {
value = node.value
bucket.removeAt(node, prev)
// 缩容
if part.size <= 0 && part != me.partitions {
me.removePartition(part)
}
me.size--
me.version++
return ok, value
} else {
return false, nil
}
}
func (me *tHashMap) removePartition(part *tPartition) {
prev := part.prev
next := part.next
if prev != nil {
prev.next = next
}
if next != nil {
next.prev = prev
}
if me.partitions == part {
me.partitions = next
}
}
func (me *tHashMap) Clear() {
if me.IsEmpty() {
return
}
part := newPartition(me.hasher, len(me.partitions.buckets))
me.partitions = part
me.size = 0
me.version++
}
func (me *tHashMap) Iterator() IMapIterator {
return newHashMapIterator(me)
}
func (me *tHashMap) String() string {
itemStrings := make([]string, 0)
for p := me.partitions;p != nil;p = p.next {
itemStrings = append(itemStrings, p.String())
}
return fmt.Sprintf("s=%v,v=%v %s", me.size, me.version, strings.Join(itemStrings, " "))
}tPartition.go
哈希表分区. 其大小呈2次幂
package hashmap
import (
"fmt"
"strings"
)
type tPartition struct {
hasher IHasher
buckets []*tBucket
bucketCount uint64
prev *tPartition
next *tPartition
size int
threshhold int
}
func newPartition(hasher IHasher, bucketCount int) *tPartition {
it := &tPartition{
hasher: hasher,
buckets: make([]*tBucket, bucketCount),
bucketCount: uint64(bucketCount),
prev: nil,
next: nil,
size: 0,
threshhold: bucketCount * 3 / 4,
}
for i,_ := range it.buckets {
it.buckets[i] = newBucket(hasher)
}
return it
}
func (me *tPartition) putByKey(key interface{}, value interface{}) bool {
hash := me.hasher.Hash(key)
return me.putByKeyAndHash(key, value, hash)
}
func (me *tPartition) putByKeyAndHash(key interface{}, value interface{}, hash uint64) bool {
if me.getBucketByHash(hash).put(key, value) {
me.size++
return true
}
return false
}
func (me *tPartition) appendByKeyAndHash(key interface{}, value interface{}, hash uint64) {
me.getBucketByHash(hash).append(key, value)
me.size++
}
func (me *tPartition) getBucketByKey(key interface{}) *tBucket {
hash := me.hasher.Hash(key)
return me.getBucketByHash(hash)
}
func (me *tPartition) getBucketByHash(hash uint64) *tBucket {
return me.buckets[int(hash % me.bucketCount)]
}
func (me *tPartition) get(key interface{}) (bool,interface{}) {
return me.getBucketByKey(key).get(key)
}
func (me *tPartition) findByKey(key interface{}) (ok bool,bucket *tBucket,node *tLinkedNode, prev *tLinkedNode) {
bucket = me.getBucketByKey(key)
ok,node,prev = bucket.find(key)
return ok,bucket,node, prev
}
func (me *tPartition) findByKeyAndHash(key interface{}, hash uint64) (ok bool,bucket *tBucket,node *tLinkedNode, prev *tLinkedNode) {
bucket = me.getBucketByHash(hash)
ok,node,prev = bucket.find(key)
return ok,bucket,node, prev
}
func (me *tPartition) remove(key interface{}) (bool, value interface{}) {
ok,node := me.getBucketByKey(key).remove(key)
if ok {
me.size--
return true, node.value
} else {
return false, nil
}
}
func (me *tPartition) nearlyFull() bool {
return me.size >= me.threshhold
}
func (me *tPartition) String() string {
itemStrings := make([]string, 0)
for i,b := range me.buckets {
if b.size > 0 {
itemStrings = append(itemStrings, fmt.Sprintf("%v:%s", i, b.String()))
}
}
return fmt.Sprintf("p[%s]", strings.Join(itemStrings, ","))
}tBucket.go
哈希桶, 每个桶内的任何元素, 哈希值是一致的
package hashmap
import (
"fmt"
"strings"
)
type tBucket struct {
hasher IHasher
nodes *tLinkedNode
size int
}
type tLinkedNode struct {
key interface{}
value interface{}
next *tLinkedNode
}
func newBucket(hasher IHasher) *tBucket {
return &tBucket{
hasher: hasher,
nodes: nil,
size: 0,
}
}
func newLinkedNode(key interface{}, value interface{}) *tLinkedNode {
return &tLinkedNode{
key: key,
value: value,
next: nil,
}
}
func (me *tBucket) put(key interface{}, value interface{}) bool {
existed, node, _ := me.find(key)
me.putAt(node, key, value)
return !existed
}
func (me *tBucket) append(key interface{}, value interface{}) {
me.putAt(nil, key, value)
}
func (me *tBucket) putAt(node *tLinkedNode, key interface{}, value interface{}) {
if node != nil {
node.value = value
return
}
it := newLinkedNode(key, value)
if me.nodes == nil {
me.nodes = it
} else {
it.next = me.nodes
me.nodes = it
}
me.size++
}
func (me *tBucket) get(key interface{}) (bool, interface{}) {
ok, node, _ := me.find(key)
if ok {
return true, node.value
}
return false, nil
}
func (me *tBucket) find(key interface{}) (ok bool, node *tLinkedNode, prev *tLinkedNode) {
prev = nil
for it:=me.nodes;it != nil;it = it.next {
if me.hasher.Equals(it.key, key) {
return true, it, prev
}
prev = it
}
return false, nil, nil
}
func (me *tBucket) remove(key interface{}) (bool, *tLinkedNode) {
ok,node, prev := me.find(key)
if !ok {
return false, nil
}
me.removeAt(node, prev)
return true, node
}
func (me *tBucket) removeAt(node *tLinkedNode, prev *tLinkedNode) {
if prev == nil {
me.nodes = node.next
} else {
prev.next = node.next
}
me.size--
}
func (me *tBucket) String() string {
itemStrings := make([]string, me.size)
i := 0
for it := me.nodes;it != nil;it = it.next {
itemStrings[i] = fmt.Sprintf("%v", it.key)
i++
}
return fmt.Sprintf("b[%v %s]", me.size, strings.Join(itemStrings, ","))
}tHashMapIterator.go
哈希表迭代器的实现
package hashmap
import "errors"
type tHashMapIterator struct {
hashMap *tHashMap
pindex *tPartition
bindex int
nindex *tLinkedNode
version int
visited int
}
func newHashMapIterator(hashMap *tHashMap) IMapIterator {
return &tHashMapIterator{
hashMap: hashMap,
pindex: hashMap.partitions,
bindex: -1,
nindex: nil,
version: hashMap.version,
visited: 0,
}
}
func (me *tHashMapIterator) nextNode() *tLinkedNode {
node := me.nindex
for {
if node == nil {
bkt := me.nextBucket()
if bkt == nil {
return nil
} else {
me.nindex = bkt.nodes
return me.nindex
}
} else {
node = node.next
if node != nil {
me.nindex = node
return node
}
}
}
}
func (me *tHashMapIterator) nextBucket() *tBucket {
part := me.pindex
bi := me.bindex + 1
for {
if bi >= len(part.buckets) {
part = me.nextPartition()
if part == nil {
return nil
}
bi = 0
}
bkt := part.buckets[bi]
if bkt.nodes != nil {
me.bindex = bi
return bkt
}
bi++
}
}
func (me *tHashMapIterator) nextPartition() *tPartition {
if me.pindex == nil {
return nil
}
me.pindex = me.pindex.next
return me.pindex
}
func (me *tHashMapIterator) More() bool {
if me.version != me.hashMap.version {
return false
}
return me.visited < me.hashMap.size
}
func (me *tHashMapIterator) Next() (err error, key interface{}, value interface{}) {
if me.version != me.hashMap.version {
return gConcurrentModificationError, nil, nil
}
if !me.More() {
return gNoMoreElementsError, nil, nil
}
node := me.nextNode()
if node == nil {
return gNoMoreElementsError, nil, nil
} else {
me.visited++
return nil, node.key, node.value
}
}
var gConcurrentModificationError = errors.New("concurrent modification error")
var gNoMoreElementsError = errors.New("no more elements")感谢各位的阅读，以上就是“golang基本数据结构与算法之如何使用哈希表”的内容了，经过本文的学习后，相信大家对golang基本数据结构与算法之如何使用哈希表这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是创新互联，小编将为大家推送更多相关知识点的文章，欢迎关注！
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