golang map 类型

code

1. map 循环

package main

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

func main() {
    rand.Seed(time.Now().UnixNano())

    var a map[string]int = make(map[string]int, 1024)

    for i := 0; i < 128; i++ {
        key := fmt.Sprintf("stu%d", i)
        value := rand.Intn(1000)
        a[key] = value
    }

    for key, value := range a {
        fmt.Printf("map[%s]=%d\n", key, value)
    }
}

2. map拷贝

package main

import (
    "fmt"
)

func modify(a map[string]int) {
    a["modify001"] = 1000
}

func main() {
    var a map[string]int
    fmt.Printf("a:%v\n", a)
    // a["stu01"] = 100 # map 没有进行初始化，会发生 panic

    a = make(map[string]int, 16)
    a["stu01"] = 1000
    a["stu02"] = 1000
    a["stu02"] = 1000
    a["stu03"] = 1000
    fmt.Printf("a=%#v\n", a)

    b := a
    b["stu03"] = 2000
    fmt.Printf("after modify a:%v\n", a)
    modify(a)
    fmt.Printf("after modify a:%v\n", a)
}

3. map 删除

package main

import (
    "fmt"
)

func main() {
    var a map[string]int
    fmt.Printf("a:%v\n", a)
    //a["stu01"] = 100
    a = make(map[string]int, 16)
    fmt.Printf("a=%v\n", a)
    a["stu01"] = 1000
    a["stu02"] = 1000
    a["stu03"] = 1000
    fmt.Printf("a=%#v\n", a)
    delete(a, "stu02")
    fmt.Printf("a=%#v\n", a)

    for key, _ := range a {
        delete(a, key)
    }
    fmt.Printf("after delete a=%#v\n", a)
}

4. 判断 map 是否存在

package main

import (
    "fmt"
)

func main() {
    var a map[string]int

    a = make(map[string]int, 16)
    a["stu01"] = 1000
    a["stu02"] = 1000
    a["stu03"] = 1000
    fmt.Printf("a=%#v\n", a)

    var (
        result int
        ok     bool
    )
    result, ok = a["stu03"]
    if !ok {
        fmt.Printf("key %s is not exist\n", "stu03")
    } else {
        fmt.Printf("key %s is %d\n", "stu03", result)
    }
}

5. map 初始化

package main

import (
    "fmt"
)

func main() {
    var a map[string]int = map[string]int{
        "stu01": 100,
        "stu02": 2000,
        "stu03": 300,
    }

    fmt.Println(a)
    a["stu01"] = 88888
    a["stu04"] = 38333
    fmt.Println(a)

    var key string = "stu04"
    fmt.Printf("the value of  key[%s] is :%d\n", key, a[key])
}

6. nil map

package main

import (
    "fmt"
)

func main() {
    var a map[string]int
    fmt.Printf("a:%v\n",a)

    a = make(map[string]int,16)
    a["stu01"] = 1000
    a["stu02"] = 2000
    a["stu03"] = 3000
    fmt.Printf("a=%#v\n",a)
}

7. map slice

package main

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

func mapSlice() {
    rand.Seed(time.Now().UnixNano())
    var s map[string][]int
    s = make(map[string][]int, 16)
    key := "stu01"
    value, ok := s[key]
    if !ok {
        s[key] = make([]int, 0, 16)
        value = s[key]
    }
    value = append(value, 100)
    value = append(value, 200)
    value = append(value, 300)
    s[key] = value
    fmt.Printf("map:%v\n", s)
}

func sliceMap() {
    rand.Seed(time.Now().UnixNano())
    var s []map[string]int
    s = make([]map[string]int, 5, 16)
    for index, val := range s {
        fmt.Printf("slice[%d]=%v\n", index, val)
    }

    fmt.Println()
    s[0] = make(map[string]int, 16)
    s[0]["stu01"] = 1000
    s[0]["stu02"] = 1000
    s[0]["stu03"] = 1000
}

func main() {
    mapSlice()
    sliceMap()
}

8. map sort

package main

import (
    "fmt"
    "math/rand"
    "sort"
    "time"
)

func main() {
    rand.Seed(time.Now().UnixNano())
    var a map[string]int = make(map[string]int,1024)

    for i := 0; i < 128; i++ {
        key := fmt.Sprintf("stu%d", i)
        value := rand.Intn(1000)
        a[key] = value
    }

    var keys []string = make([]string, 0, 128)
    for key,_ := range a {
        //fmt.Printf("map[%s]=%d\n",key,value)
        keys = append(keys,key)
    }
    sort.Strings(keys)
    for _,value := range keys {
        fmt.Printf("key:%s val:%d\n", value, a[value])
    }
}

课后练习

1. 写一个程序，统计一个字符串每个单词出现的次数。比如： s = “how do you do”, 输出 how = 1 do = 2 you = 1

package main

import (
    "fmt"
    "strings"
)

func statWordCount(str string) (result map[string]int) {
    words := strings.Split(str, " ")
    result = make(map[string]int, len(words))
    for _, v := range words {
        count, ok := result[v]
        if !ok {
            result[v] = 1
        } else {
            result[v] = count + 1
        }
    }
    return result
}

func main() {
    var str = "how do you do ? do you like me ?"
    result := statWordCount(str)
    fmt.Printf("result:%#v\n", result)
}

2. 写一个，实现学生信息的存储，学生有 ID 、年龄、分数等信息。需要非常方便的用过 ID 查找到对应的学生的信息。

package main

import (
    "fmt"
    "math/rand"
)

func testInterface() {
    var a interface{}
    var b int = 100
    var c float32 = 1.2
    var d string = "hello"

    a = b
    fmt.Printf("a=%v\n", a)

    a = c
    fmt.Printf("a=%v\n", a)

    a = d
    fmt.Printf("a=%v\n", a)
}

func studentStore() {
    var stuMap map[int]map[string]interface{}
    stuMap = make(map[int]map[string]interface{}, 16)
    //插入学生id=1，姓名=stu01, 分数=78.2, 年龄= 18
    var id = 1
    var name = "stu01"
    var score = 78.2
    var age = 18

    value, ok := stuMap[id]
    if !ok {
        value = make(map[string]interface{}, 8)
    }

    value["name"] = name
    value["id"] = id
    value["score"] = score
    value["age"] = age
    stuMap[id] = value

    fmt.Printf("stuMap:%#v\n", stuMap)

    for i := 0; i < 10; i++ {
        value, ok := stuMap[i]
        if !ok {
            value = make(map[string]interface{}, 8)
        }

        value["name"] = fmt.Sprintf("stu%d", i)
        value["id"] = i
        value["score"] = rand.Float32() * 100.0
        value["age"] = rand.Intn(100)
        stuMap[i] = value
    }

    fmt.Println()
    for k, v := range stuMap {
        fmt.Printf("id=%d stu info=%#v\n", k, v)
    }
}

func main() {
    //testInterface()
    studentStore()
}