367 lines
8.0 KiB
Go
367 lines
8.0 KiB
Go
package main
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import (
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"encoding/json"
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"fmt"
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"sort"
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"sync"
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"time"
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)
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// 3.1 数组示例
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func arrayExamples() {
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fmt.Println("=== 数组示例 ===")
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// 声明数组
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var arr1 [5]int
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arr2 := [3]string{"A", "B", "C"}
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arr3 := [4]int{10, 20, 30, 40}
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arr4 := [5]int{1, 2} // 部分初始化
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arr5 := [...]int{1, 2, 3, 4, 5}
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fmt.Printf("arr1: %v\n", arr1)
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fmt.Printf("arr2: %v\n", arr2)
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fmt.Printf("arr3: %v\n", arr3)
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fmt.Printf("arr4: %v\n", arr4)
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fmt.Printf("arr5: %v\n", arr5)
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// 访问和修改
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arr1[0] = 99
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fmt.Printf("修改后 arr1: %v\n", arr1)
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// 多维数组
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matrix := [2][3]int{
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{1, 2, 3},
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{4, 5, 6},
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}
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fmt.Printf("matrix[0][1]: %d\n", matrix[0][1])
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}
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// 3.2 切片示例
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func sliceExamples() {
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fmt.Println("\n=== 切片示例 ===")
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// 从数组创建
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arr := [5]int{1, 2, 3, 4, 5}
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s1 := arr[0:3]
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s2 := arr[1:]
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s3 := arr[:3]
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s4 := arr[:]
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fmt.Printf("s1: %v, len=%d, cap=%d\n", s1, len(s1), cap(s1))
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fmt.Printf("s2: %v, len=%d, cap=%d\n", s2, len(s2), cap(s2))
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fmt.Printf("s3: %v, len=%d, cap=%d\n", s3, len(s3), cap(s3))
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fmt.Printf("s4: %v, len=%d, cap=%d\n", s4, len(s4), cap(s4))
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// make 创建
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s5 := make([]int, 5)
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s6 := make([]int, 3, 10)
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fmt.Printf("s5: %v, len=%d, cap=%d\n", s5, len(s5), cap(s5))
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fmt.Printf("s6: %v, len=%d, cap=%d\n", s6, len(s6), cap(s6))
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// append
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s7 := []int{1, 2, 3}
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s7 = append(s7, 4)
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s7 = append(s7, 5, 6, 7)
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s8 := []int{8, 9, 10}
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s7 = append(s7, s8...)
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fmt.Printf("s7 after append: %v\n", s7)
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// 容量变化演示
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fmt.Println("\n容量变化:")
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s9 := make([]int, 0, 5)
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for i := 1; i <= 10; i++ {
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s9 = append(s9, i)
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fmt.Printf("追加 %d: len=%d, cap=%d\n", i, len(s9), cap(s9))
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}
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// copy
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src := []int{1, 2, 3, 4, 5}
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dst := make([]int, 3)
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n := copy(dst, src)
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fmt.Printf("\n复制了 %d 个元素，dst: %v\n", n, dst)
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// 共享底层数组陷阱
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s10 := []int{1, 2, 3, 4, 5}
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s11 := s10[1:3]
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s11[0] = 99
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fmt.Printf("\n共享数组陷阱:\n")
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fmt.Printf("s10: %v\n", s10)
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fmt.Printf("s11: %v\n", s11)
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// 释放内存的正确方式
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fmt.Println("\n释放内存:")
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data := make([]int, 1000)
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small := append([]int(nil), data[:10]...)
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fmt.Printf("small cap: %d (原 data cap: %d)\n", cap(small), cap(data))
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}
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// 3.3 映射示例
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func mapExamples() {
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fmt.Println("\n=== 映射示例 ===")
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// 创建映射
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m1 := make(map[string]int)
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m1["one"] = 1
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m1["two"] = 2
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m2 := map[string]int{
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"one": 1,
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"two": 2,
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"three": 3,
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}
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fmt.Printf("m1: %v\n", m1)
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fmt.Printf("m2: %v\n", m2)
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// 读取和检查存在
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value, exists := m2["two"]
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fmt.Printf("two 存在： %v, 值： %d\n", exists, value)
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value, exists = m2["four"]
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fmt.Printf("four 存在： %v, 值： %d\n", exists, value)
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// 删除
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delete(m2, "one")
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fmt.Printf("删除 one 后： %v\n", m2)
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// 遍历（无序）
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fmt.Println("\n遍历映射:")
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for k, v := range m2 {
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fmt.Printf("%s: %d\n", k, v)
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}
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// nil 映射
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var m3 map[string]int
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fmt.Printf("\nnil 映射读取： %d\n", m3["key"])
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// m3["key"] = 1 // panic!
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// 嵌套映射
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scores := map[string]map[string]int{
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"Alice": {"math": 95, "english": 88},
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"Bob": {"math": 92, "english": 90},
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}
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fmt.Printf("\nAlice 数学成绩： %d\n", scores["Alice"]["math"])
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// 动态创建
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if scores["Charlie"] == nil {
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scores["Charlie"] = make(map[string]int)
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}
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scores["Charlie"]["math"] = 85
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fmt.Printf("Charlie 数学成绩： %d\n", scores["Charlie"]["math"])
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}
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// 3.4 结构体示例
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func structExamples() {
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fmt.Println("\n=== 结构体示例 ===")
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// 定义结构体
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type Person struct {
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Name string
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Age int
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Email string
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}
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// 初始化
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p1 := Person{Name: "Alice", Age: 25, Email: "alice@example.com"}
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p2 := Person{"Bob", 30, "bob@example.com"}
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p3 := Person{Name: "Charlie"}
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p4 := &Person{Name: "David", Age: 28}
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fmt.Printf("p1: %+v\n", p1)
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fmt.Printf("p2: %+v\n", p2)
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fmt.Printf("p3: %+v\n", p3)
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fmt.Printf("p4: %+v\n", *p4)
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// 方法
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type Rectangle struct {
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Width float64
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Height float64
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}
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rect := Rectangle{Width: 10, Height: 5}
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// 定义方法（在函数外定义）
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area := rect.Width * rect.Height
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fmt.Printf("矩形面积： %.2f\n", area)
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// 嵌入
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type Employee struct {
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Person
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ID int
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Salary float64
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}
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e := Employee{
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Person: Person{Name: "Eve", Age: 35},
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ID: 1001,
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Salary: 50000,
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}
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fmt.Printf("员工姓名： %s\n", e.Name) // 直接访问嵌入字段
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fmt.Printf("员工 ID: %d\n", e.ID)
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// 结构体标签
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type User struct {
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ID int `json:"id"`
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Name string `json:"name"`
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Email string `json:"email,omitempty"`
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Password string `json:"-"`
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}
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user := User{ID: 1, Name: "Alice", Email: "alice@example.com", Password: "secret"}
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jsonData, _ := json.Marshal(user)
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fmt.Printf("JSON: %s\n", jsonData)
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}
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// 3.5 学生管理系统
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type Student struct {
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ID int `json:"id"`
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Name string `json:"name"`
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Age int `json:"age"`
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Score float64 `json:"score"`
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}
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type StudentManager struct {
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students map[int]*Student
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nextID int
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}
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func NewStudentManager() *StudentManager {
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return &StudentManager{
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students: make(map[int]*Student),
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nextID: 1,
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}
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}
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func (sm *StudentManager) AddStudent(name string, age int, score float64) int {
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id := sm.nextID
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sm.nextID++
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sm.students[id] = &Student{ID: id, Name: name, Age: age, Score: score}
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return id
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}
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func (sm *StudentManager) GetStudent(id int) *Student {
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return sm.students[id]
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}
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func (sm *StudentManager) UpdateStudent(id int, name string, age int, score float64) bool {
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if student, exists := sm.students[id]; exists {
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student.Name = name
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student.Age = age
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student.Score = score
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return true
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}
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return false
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}
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func (sm *StudentManager) DeleteStudent(id int) bool {
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if _, exists := sm.students[id]; exists {
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delete(sm.students, id)
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return true
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}
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return false
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}
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func (sm *StudentManager) GetAllStudents() []*Student {
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students := make([]*Student, 0, len(sm.students))
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for _, s := range sm.students {
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students = append(students, s)
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}
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return students
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}
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func (sm *StudentManager) SortByScore(descending bool) []*Student {
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students := sm.GetAllStudents()
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sort.Slice(students, func(i, j int) bool {
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if descending {
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return students[i].Score > students[j].Score
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}
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return students[i].Score < students[j].Score
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})
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return students
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}
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func studentManagerDemo() {
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fmt.Println("\n=== 学生管理系统 ===")
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manager := NewStudentManager()
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id1 := manager.AddStudent("Alice", 20, 95.5)
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id2 := manager.AddStudent("Bob", 22, 88.0)
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id3 := manager.AddStudent("Charlie", 21, 92.5)
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fmt.Printf("添加学生 ID: %d, %d, %d\n", id1, id2, id3)
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manager.UpdateStudent(id1, "Alice", 21, 97.0)
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fmt.Printf("更新后 Alice: %+v\n", manager.GetStudent(id1))
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manager.DeleteStudent(id2)
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fmt.Printf("删除后学生数量： %d\n", len(manager.GetAllStudents()))
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sorted := manager.SortByScore(true)
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fmt.Println("\n按分数降序排列:")
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for _, s := range sorted {
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fmt.Printf(" %s: %.1f\n", s.Name, s.Score)
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}
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jsonStr, _ := json.MarshalIndent(manager.students, "", " ")
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fmt.Println("\nJSON 导出:")
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fmt.Println(string(jsonStr))
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}
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// 3.6 性能对比
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func slicePerformance() {
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fmt.Println("\n=== 切片性能对比 ===")
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// 预分配容量
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start := time.Now()
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s1 := make([]int, 0, 10000)
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for i := 0; i < 10000; i++ {
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s1 = append(s1, i)
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}
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fmt.Printf("预分配容量耗时： %v\n", time.Since(start))
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// 不预分配容量
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start = time.Now()
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s2 := make([]int, 0)
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for i := 0; i < 10000; i++ {
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s2 = append(s2, i)
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}
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fmt.Printf("不预分配容量耗时： %v\n", time.Since(start))
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}
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// 3.7 并发安全映射
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func concurrentMapDemo() {
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fmt.Println("\n=== 并发安全映射 ===")
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var m = make(map[string]int)
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var mu sync.RWMutex
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var wg sync.WaitGroup
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// 写操作
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for i := 0; i < 100; i++ {
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wg.Add(1)
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go func(id int) {
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defer wg.Done()
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mu.Lock()
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m[fmt.Sprintf("key%d", id%10)] = id
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mu.Unlock()
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}(i)
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}
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wg.Wait()
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fmt.Printf("最终映射大小： %d\n", len(m))
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}
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func main() {
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arrayExamples()
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sliceExamples()
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mapExamples()
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structExamples()
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studentManagerDemo()
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slicePerformance()
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concurrentMapDemo()
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}
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