GO语言系列- 高级数据类型之数组、切片、map

一、数组和切片

数组

• 1. 数组：是同一种数据类型的固定长度的序列。
• 2. 数组定义：var a [len]int，比如：var a[5]int，一旦定义，长度不能变
• 3. 长度是数组类型的一部分，因此，var a[5] int和var a[10]int是不同的类型
• 4. 数组可以通过下标进行访问，下标是从0开始，最后一个元素下标是：len-1

for i := 0; i < len(a); i++ {
}
for index, v := range a {
}

• 5. 访问越界，如果下标在数组合法范围之外，则触发访问越界，会panic
• 6. 数组是值类型，因此改变副本的值，不会改变本身的值

package main

import "fmt"

func test1() {
    var a [10]int
    a[0] = 10
    a[9] = 100
    fmt.Println(a)

    for i := 0; i < len(a); i++ {
        fmt.Println(a[i])
    }
    for index, val := range a {
        fmt.Printf("a[%d]=%d
", index, val)
    }
}

func test2() {
    var a [10]int
    b := a
    b[0] = 100
    fmt.Println(a)
}

func test3(arr *[5]int) {
    (*arr)[0] = 1000
}

func main() {
    test1()
    test2()
    var a [5]int
    test3(&a)
    fmt.Println(a)
}

/*
[10 0 0 0 0 0 0 0 0 100]
10
0
0
0
0
0
0
0
0
100
a[0]=10
a[1]=0
a[2]=0
a[3]=0
a[4]=0
a[5]=0
a[6]=0
a[7]=0
a[8]=0
a[9]=100
[0 0 0 0 0 0 0 0 0 0]
[1000 0 0 0 0]
*/

数组初始化

a. var age0 [5]int = [5]int{1,2,3}
b. var age1 = [5]int{1,2,3,4,5}
c. var age2 = […]int{1,2,3,4,5,6}
d. var str = [5]string{3:”hello world”, 4:”tom”}

多维数组

a. var age [5][3]int
b. var f [2][3]int = [...][3]int{{1, 2, 3}, {7, 8, 9}}　　

多维数组遍历

package main

import (
	"fmt"
)

func main() {

	var f [2][3]int = [...][3]int{{1, 2, 3}, {7, 8, 9}}

	for k1, v1 := range f {
		for k2, v2 := range v1 {
			fmt.Printf("(%d,%d)=%d ", k1, k2, v2)
		}
		fmt.Println()
	}
}　

数组示例

package main

import (
    "fmt"
)

func fab(n int) {
    var a []int
    a = make([]int, n)

    a[0] = 1
    a[1] = 1

    for i := 2; i < n; i++ {
        a[i] = a[i-1] + a[i-2]
    }

    for _, v := range a {
        fmt.Println(v)
    }
}

func testArray() {
    var a [5]int = [5]int{1, 2, 3, 4, 5}
    var a1 = [5]int{1, 2, 3, 4, 5}
    var a2 = [...]int{38, 283, 48, 38, 348, 387, 484}
    var a3 = [...]int{1: 100, 3: 200}
    var a4 = [...]string{1: "hello", 3: "world"}

    fmt.Println(a)
    fmt.Println(a1)
    fmt.Println(a2)
    fmt.Println(a3)
    fmt.Println(a4)
    /*
        [1 2 3 4 5]
        [1 2 3 4 5]
        [38 283 48 38 348 387 484]
        [0 100 0 200]
        [ hello  world]
    */
}

func testArray2() {
    var a [2][5]int = [...][5]int{{1, 2, 3, 4, 5}, {6, 7, 8, 9, 10}}

    for row, v := range a {
        for col, v1 := range v {
            fmt.Printf("(%d,%d)=%d ", row, col, v1)
        }
        fmt.Println()
    }
}

func main() {
    fab(10)
    testArray()
    testArray2()
}

切片

1. 切片相关概念

• 1. 切片：切片是数组的一个引用，因此切片是引用类型
• 2. 切片的长度可以改变，因此，切片是一个可变的数组
• 3. 切片遍历方式和数组一样，可以用len()求长度
• 4. cap可以求出slice最大的容量，0 <= len(slice) <= (array)，其中array是slice引用的数组
• 5. 切片的定义：var 变量名 []类型，比如 var str []string var arr []int

2. 切片的相关语法

• 1. 切片初始化：var slice []int = arr[start:end] 包含start到end之间的元素，但不包含end
• 2. Var slice []int = arr[0:end]可以简写为 var slice []int=arr[:end]
• 3. Var slice []int = arr[start:len(arr)] 可以简写为 var slice[]int = arr[start:]
• 4. Var slice []int = arr[0, len(arr)] 可以简写为 var slice[]int = arr[:]
• 5. 如果要切片最后一个元素去掉，可以这么写： Slice = slice[:len(slice)-1]

3. 切片的内存布局

4. 通过make来创建切片

var slice []type = make([]type, len)
slice := make([]type, len)
slice := make([]type, len, cap)

5. 用append内置函数操作切片

slice = append(slice, 10)
var a = []int{1,2,3}
var b = []int{4,5,6}
a = append(a, b…)

6. For range 遍历切片

for index, val := range slice {
}

7. 切片resize

var a = []int {1,3,4,5}
b := a[1:2]
b = b[0:3]

8. 切片拷贝

s1 := []int{1,2,3,4,5}

s2 := make([]int, 10)

copy(s2, s1)

s3 := []int{1,2,3}

s3 = append(s3, s2…)

s3 = append(s3, 4,5,6)

9. string与slice

　　string底层就是一个byte的数组，因此，也可以进行切片操作

str := “hello world”
s1 := str[0:5]
fmt.Println(s1)
s2 := str[5:]
fmt.Println(s2)

10. string的底层布局

11. 如何改变string中的字符值？

string本身是不可变的，因此要改变string中字符，需要如下操作：

str := “hello world”
s := []byte(str)
s[0] = ‘o’
str = string(s)

12. 排序和查找操作

排序操作主要都在 sort包中，导入就可以使用了

sort.Ints对整数进行排序， sort.Strings对字符串进行排序, sort.Float64s对
浮点数进行排序.
sort.SearchInts(a []int, b int) 从数组a中查找b，前提是a必须有序
sort.SearchFloats(a []float64, b float64) 从数组a中查找b，前提是a必须有序
sort.SearchStrings(a []string, b string) 从数组a中查找b，前提是a必须有序

13. 切片的扩容机制

可以通过查看$GOROOT/src/runtime/slice.go源码，其中扩容相关代码如下：

newcap := old.cap
doublecap := newcap + newcap
if cap > doublecap {
	newcap = cap
} else {
	if old.len < 1024 {
		newcap = doublecap
	} else {
		// Check 0 < newcap to detect overflow
		// and prevent an infinite loop.
		for 0 < newcap && newcap < cap {
			newcap += newcap / 4
		}
		// Set newcap to the requested cap when
		// the newcap calculation overflowed.
		if newcap <= 0 {
			newcap = cap
		}
	}
}

从上面的代码可以看出以下内容：

• 首先判断，如果新申请容量（cap）大于2倍的旧容量（old.cap），最终容量（newcap）就是新申请的容量（cap）。
• 否则判断，如果旧切片的长度小于1024，则最终容量(newcap)就是旧容量(old.cap)的两倍，即（newcap=doublecap），
• 否则判断，如果旧切片长度大于等于1024，则最终容量（newcap）从旧容量（old.cap）开始循环增加原来的1/4，即（newcap=old.cap,for {newcap += newcap/4}）直到最终容量（newcap）大于等于新申请的容量(cap)，即（newcap >= cap）
• 如果最终容量（cap）计算值溢出，则最终容量（cap）就是新申请容量（cap）。

需要注意的是，切片扩容还会根据切片中元素的类型不同而做不同的处理，比如int和string类型的处理方式就不一样。

示例

package main

import "fmt"

type slice struct {
    ptr *[100]int
    len int
    cap int
}

func make1(s slice, cap int) slice {
    s.ptr = new([100]int)
    s.cap = cap
    s.len = 0
    return s
}

func testSlice() {
    var slice []int
    var arr [5]int = [...]int{1, 2, 3, 4, 5}

    slice = arr[:]
    fmt.Println(slice)
    fmt.Println(arr[2:4]) // [3,4]
    fmt.Println(arr[2:])  // [3,4,5]
    fmt.Println(arr[0:1]) // [1]
    fmt.Println(arr[:len(arr)-1])
}

func modify(s slice) {
    s.ptr[1] = 1000
}

func testSlice2() {
    var s1 slice
    s1 = make1(s1, 10)

    s1.ptr[0] = 100
    modify(s1)

    fmt.Println(s1.ptr)
}

func modify1(a []int) {
    a[1] = 1000
}

func testSlice3() {
    var b []int = []int{1, 2, 3, 4}
    modify1(b)
    fmt.Println(b)
}

func testSlcie4() {
    var a = [10]int{1, 2, 3, 4}

    b := a[1:5]
    fmt.Printf("%p
", b)     // 0xc000014238
    fmt.Printf("%p
", &a[1]) // 0xc000014238
}

func main() {
    // testSlice()
    testSlice2()
    testSlice3()
    testSlcie4()
}

package main

import "fmt"

func testSlice() {
    var a [5]int = [...]int{1, 2, 3, 4, 5}
    s := a[1:]
    fmt.Println("a:", a)
    s[1] = 100
    fmt.Printf("s=%p a[1]=%p
", s, &a[1])
    fmt.Println("before a:", a)

    s = append(s, 10)
    s = append(s, 10)
    s = append(s, 10)
    s = append(s, 10)
    s = append(s, 10)

    s[1] = 1000
    fmt.Println("after a:", a)
    fmt.Println(s)
    fmt.Printf("s=%p a[1]=%p
", s, &a[1])
}

func testCopy() {
    var a []int = []int{1, 2, 3, 4, 5}
    b := make([]int, 10)

    copy(b, a)

    fmt.Println(b)
}

func testString() {
    s := "hello world"
    s1 := s[0:5]
    s2 := s[6:]

    fmt.Println(s1)
    fmt.Println(s2)
}

func testModifyString() {
    s := "我hello world"
    s1 := []rune(s)

    s1[0] = 200
    s1[1] = 128
    s1[2] = 256
    str := string(s1)
    fmt.Println(str)
}

func main() {
    // testSlice()
    testCopy()
    testString()
    testModifyString()
}

package main

import (
    "fmt"
    "sort"
)

func testIntSort() {
    var a = [...]int{1, 8, 43, 2, 456}
    sort.Ints(a[:])
    fmt.Println(a)
}

func testStrings() {
    var a = [...]string{"abc", "efg", "b", "A", "eeee"}
    sort.Strings(a[:])

    fmt.Println(a)
}

func testFloat() {
    var a = [...]float64{2.3, 0.8, 28.2, 392342.2, 0.6}
    sort.Float64s(a[:])
    fmt.Println(a)
}

func testIntSearch() {
    var a = [...]int{1, 8, 43, 2, 456}
    index := sort.SearchInts(a[:], 2)
    fmt.Println(index)
}

func main() {
    testIntSort()
    testStrings()
    testFloat()
    testIntSearch()
}

二、map数据结构

1.map简介

key-value的数据结构，又叫字典或关联数组
a.声明

var map1 map[keytype]valuetype
var a map[string]string
var a map[string]int
var a map[int]string
var a map[string]map[string]string

声明是不会分配内存的，初始化需要make

2. map相关操作

var a map[string]string = map[string]string{“hello”: “world”}
a = make(map[string]string, 10)
a[“hello”] = “world”	// 插入和更新
Val, ok := a[“hello”]	//查找
for k, v := range a {	//遍历
fmt.Println(k,v)
}
delete(a, “hello”)	// 删除
len(a)	// 长度

3. map是引用类型

func modify(a map[string]int) {
a[“one”] = 134
}

4. slice of map

Items := make([]map[int][int], 5)
For I := 0; I < 5; i++ {
items[i] = make(map[int][int])
}

5. map排序

a. 先获取所有key，把key进行排序
b. 按照排序好的key，进行遍历

6. Map反转

• a. 初始化另外一个map，把key、value互换即可

 示例

package main

import "fmt"

func trans(a map[string]map[string]string) {
    for k, v := range a {
        fmt.Println(k)
        for k1, v1 := range v {
            fmt.Println("	", k1, v1)
        }
    }
}

func testMap() {
    var a map[string]string = map[string]string{
        "key": "value",
    }
    // a := make(map[string]string, 10)
    a["abc"] = "efg"
    a["abc1"] = "wew"
    fmt.Println(a)
}

func testMap2() {
    a := make(map[string]map[string]string, 100)
    a["key1"] = make(map[string]string)
    a["key1"]["key2"] = "val2"
    a["key1"]["key3"] = "val3"
    a["key1"]["key4"] = "val4"
    a["key1"]["key5"] = "val5"
    a["key1"]["key6"] = "val6"
    fmt.Println(a)

}

func modify(a map[string]map[string]string) {
    _, ok := a["zhangsan"]
    if !ok {
        a["zhangsan"] = make(map[string]string)
    }
    a["zhangsan"]["pwd"] = "123456"
    a["zhangsan"]["nickname"] = "superman"
    return
}

func testMap3() {
    a := make(map[string]map[string]string, 100)
    modify(a)
    fmt.Println(a)
}

func testMap4() {
    a := make(map[string]map[string]string, 100)
    a["key1"] = make(map[string]string)
    a["key1"]["key2"] = "val2"
    a["key1"]["key3"] = "val3"
    a["key1"]["key4"] = "val4"
    a["key1"]["key5"] = "val5"
    a["key2"] = make(map[string]string)
    a["key2"]["key22"] = "val22"
    a["key2"]["key23"] = "val23"
    trans(a)
    delete(a, "key1")
    fmt.Println()
    trans(a)
}

func testMap5() {
    var a []map[int]int
    a = make([]map[int]int, 5)

    if a[0] == nil {
        a[0] = make(map[int]int)
    }
    a[0][10] = 10
    fmt.Println(a)
}

func main() {
    testMap()
    testMap2()
    testMap3()
    testMap4()
    testMap5()
}

package main

import (
    "fmt"
    "sort"
)

func testMapSort() {
    var a map[int]int
    a = make(map[int]int, 5)

    a[8] = 10
    a[3] = 10
    a[2] = 10
    a[1] = 10
    a[18] = 10

    var keys []int
    for k, _ := range a {
        keys = append(keys, k)
        // fmt.Println(k, v)
    }
    sort.Ints(keys)
    for _, v := range keys {
        fmt.Println(v, a[v])
    }
}

func testMapSort2() {
    var a map[string]int
    var b map[int]string

    a = make(map[string]int, 5)
    b = make(map[int]string, 5)
    a["8"] = 10
    a["3"] = 11
    a["2"] = 12
    a["1"] = 13
    a["18"] = 14

    for k, v := range a {
        b[v] = k
    }
    fmt.Println(b)
}

func main() {
    testMapSort()
    testMapSort2()
}

补充：golang实现集合（set）

package set
 
import (
    "bytes"
    "fmt"
    "sync"
)
 
type Set struct {
    m map[interface{}]bool
    sync.RWMutex
}
 
func New() *Set {
    return &Set{m: make(map[interface{}]bool)}
}
 
func (self *Set) Add(e interface{}) bool {
    self.Lock()
    defer self.Unlock()
    if self.m[e] {
        return false
    }
    self.m[e] = true
    return true
}
 
func (self *Set) Remove(e interface{}) bool {
    self.Lock()
    defer self.Unlock()
    delete(self.m, e)
    return true
}
 
func (self *Set) Clear() bool {
    self.Lock()
    defer self.Unlock()
    self.m = make(map[interface{}]bool)
    return true
}
 
func (self *Set) Contains(e interface{}) bool {
    self.Lock()
    defer self.Unlock()
    //return self.m[e]
    _, ok := self.m[e]
    return ok
}
 
func (self *Set) IsEmpty() bool {
    return self.Len() == 0
}
 
func (self *Set) Len() int {
    self.Lock()
    defer self.Unlock()
    return len(self.m)
}
 
func (self *Set) Same(other *Set) bool {
    if other == nil {
        return false
    }
 
    if self.Len() != other.Len() {
        return false
    }
 
    for k, _ := range other.m {
        if !self.Contains(k) {
            return false
        }
    }
    return true
}
 
func (self *Set) Elements() interface{} {
    self.Lock()
    defer self.Unlock()
    // for k := range self.m{
    //    snapshot = snapshot(snapshot, k)
    // }
    initialLen := self.Len()
    actualLen := 0
    snapshot := make([]interface{}, initialLen)
    for k := range self.m {
        if actualLen < initialLen {
            snapshot[actualLen] = k
        } else {
            snapshot = append(snapshot, k)
        }
        actualLen++
    }
    if actualLen < initialLen {
        snapshot = snapshot[:actualLen]
    }
    return snapshot
}
 
func (self *Set) String() string {
    self.Lock()
    defer self.Unlock()
    var buf bytes.Buffer
    buf.WriteString("Set{")
    flag := true
    for k := range self.m {
        if flag {
            flag = false
        } else {
            buf.WriteString(" ")
        }
        buf.WriteString(fmt.Sprintf("%v", k))
    }
    buf.WriteString("}")
 
    return buf.String()
}
 
func (self *Set) IsSuperSet(other *Set) bool {
    self.Lock()
    defer self.Unlock()
    if other == nil {
        return false
    }
    selfLen := self.Len()
    otherLen := other.Len()
    if otherLen == 0 || selfLen == otherLen {
        return false
    }
    if selfLen > 0 && otherLen == 0 {
        return true
    }
    for v := range other.m {
        if !self.Contains(v) {
            return false
        }
    }
    return true
}
 
//属于A或属于B的元素
func (self *Set) Union(other *Set) *Set {
    self.Lock()
    defer self.Unlock()
    // if other == nil || other.Len() == 0{
    //    return self
    // }
    //
    // for v := range other.m{
    //    self.Add(v)
    // }
    // return self
    //不能改变集合A的范围
    union := New()
    for v := range self.m {
        union.Add(v)
    }
    for v := range other.m {
        union.Add(v)
    }
    return union
}
 
//属于A且属于B的元素
func (self *Set) Intersect(other *Set) *Set {
    self.Lock()
    defer self.Unlock()
    if other == nil || other.Len() == 0 {
        return New()
    }
    intsSet := New()
    for v, _ := range other.m {
        if self.Contains(v) {
            intsSet.Add(v)
        }
    }
    return intsSet
}
 
//属于A且不属于B的元素
func (self *Set) Difference(other *Set) *Set {
    self.Lock()
    defer self.Unlock()
    diffSet := New()
    if other == nil || other.Len() == 0 {
        diffSet.Union(self)
    } else {
        for v := range self.m {
            if !other.Contains(v) {
                diffSet.Add(v)
            }
        }
    }
 
    return diffSet
}
 
//集合A与集合B中所有不属于A∩B的元素的集合
func (self *Set) SymmetricDifference(other *Set) *Set {
    self.Lock()
    defer self.Unlock()
    //此时A∩B=∅，A中所有元素均不属于空集
    // if other == nil || other.Len() == 0{
    //    return self
    // }
    // ints := self.Intersect(other)
    // //此时A∩B=∅，A为空或B为空,B为空前面已经判断，此时B不能为空，即A为空
    // if ints == nil || ints.Len() == 0 {
    //    return other
    // }
    //
    // unionSet := self.Union(other)
    // result := New()
    // for v := range unionSet.m{
    //    if !ints.Contains(v){
    //       result.Add(v)
    //    }
    // }
    ints := self.Difference(other)
    union := self.Union(other)
    return union.Difference(ints)
}

package main
 
import (
    "fmt"
    "go_dev/go_set/set"
)
 
func main() {
    setTest()
}
 
func setTest() {
    set1 := set.New()
    set1.Add(1)
    set1.Add("e2")
    set1.Add(3)
    set1.Add("e4")
    fmt.Println("set1:", set1)
    fmt.Printf("set1 Elements:%v
", set1.Elements())
 
    set2 := set.New()
    set2.Add(3)
    set2.Add("e2")
    set2.Add(5)
    set2.Add("e6")
 
    fmt.Println("set2:", set2)
    fmt.Printf("set1 union set2:%v
", set1.Union(set2))
    fmt.Printf("set1 intersect set2:%v
", set1.Intersect(set2))
    fmt.Println(set1,set2)
    fmt.Printf("set1 difference set2:%v
", set1.Difference(set2))
    fmt.Printf("set1 SymmetricDifference set2:%v
", set1.SymmetricDifference(set2))
    set1.Clear()
    fmt.Println(set1)
}

三、包

1. golang中的包

• a. golang目前有150个标准的包，覆盖了几乎所有的基础库

• b. golang.org有所有包的文档，没事都翻翻

2. 线程同步

a. import(“sync”)
b. 互斥锁, var mu sync.Mutex
c. 读写锁, var mu sync.RWMutex

package main

import (
    "fmt"
    "math/rand"
    "sync"
    "sync/atomic"
    "time"
)

var rwLock *sync.RWMutex

func testLock() {

    var a map[int]int
    a = make(map[int]int, 5)

    a[8] = 10
    a[3] = 10
    a[2] = 10
    a[1] = 10
    a[18] = 10

    for i := 0; i < 2; i++ {
        go func(b map[int]int) {
            rwLock.RLock()
            b[8] = rand.Intn(100)
            rwLock.Unlock()
        }(a)
    }

    rwLock.RLock()
    fmt.Println(a)
    rwLock.Unlock()
}

func testRWLock() {
    // var rwLock myLocker = new(sync.RWMutex)
    // var rwLock sync.RWMutex
    // var rwLock sync.Mutex
    var a map[int]int
    a = make(map[int]int, 5)

    var count int32

    a[8] = 10
    a[3] = 10
    a[2] = 10
    a[1] = 10
    a[18] = 10

    for i := 0; i < 2; i++ {
        go func(b map[int]int) {
            rwLock.Lock()
            // lock.Lock()
            b[8] = rand.Intn(100)
            time.Sleep(time.Millisecond)
            rwLock.Unlock()
            // lock.Unlock()
        }(a)
    }

    for i := 0; i < 100; i++ {
        go func(b map[int]int) {
            for {
                rwLock.Lock()
                time.Sleep(time.Millisecond)
                // fmt.Println(a)
                rwLock.Unlock()
                atomic.AddInt32(&count, 1)
            }
        }(a)
    }

    time.Sleep(time.Second * 3)
    fmt.Println(atomic.LoadInt32(&count))
}

func main() {
    rwLock = new(sync.RWMutex)
    // testLock()
    testRWLock()
}

3. go get安装第三方包

go get github.com/go-sql-driver/mysql 

本节作业

• 1. 冒泡排序

• 2. 选择排序

• 3. 插入排序

• 4.快速排序

参考

package main

import "fmt"

// 冒泡排序：本质上是交换排序的一种
func bsort(a []int) {
    for i := 0; i < len(a); i++ {
        for j := 1; j < len(a)-i; j++ {
            if a[j] < a[j-1] {
                a[j], a[j-1] = a[j-1], a[j]
            }
        }
    }
}

func main() {
    b := [...]int{8, 7, 4, 5, 3, 2, 1}
    bsort(b[:])
    fmt.Println(b)
}

package main

import "fmt"

// 选择排序
func ssort(a []int) {
    for i := 0; i < len(a); i++ {
        var min int = i
        for j := i + 1; j < len(a); j++ {
            if a[min] > a[j] {
                min = j
            }
        }
        if min != i {
            a[i], a[min] = a[min], a[i]
        }
    }
}

func main() {
    b := [...]int{8, 7, 4, 5, 3, 2, 1}
    ssort(b[:])
    fmt.Println(b)
}

package main

import "fmt"

// 插入排序, 每次将一个数插入到有序序列当中合适的位置
func isort(a []int) {
    for i := 1; i < len(a); i++ {
        for j := i; j > 0; j-- {
            if a[j] > a[j-1] {
                break
            }
            a[j], a[j-1] = a[j-1], a[j]
        }
    }
}

func main() {
    b := [...]int{8, 7, 4, 5, 3, 2, 1}
    isort(b[:])
    fmt.Println(b)
}

package main

import "fmt"

// 快速排序, 一次排序确定一个元素的位置， 使左边的元素都比它小，右边的元素都比它大
func qsort(a []int, left, right int) {
    if left >= right {
        return
    }
    val := a[left]
    // 确定val所在的位置
    k := left
    for i := left + 1; i <= right; i++ {
        if a[i] < val {
            a[k] = a[i]
            a[i] = a[k+1]
            k++
        }
    }
    a[k] = val
    qsort(a, left, k-1)
    qsort(a, k+1, right)
}

func main() {
    b := [...]int{8, 7, 4, 5, 3, 2, 1}
    qsort(b[:], 0, len(b)-1)
    fmt.Println(b)
}