Google资深工程师深度讲解Go语言内建容器(三)

一数组

1. 数量写在类型前面
2. 可通过_省略变量
3. 不仅range,任何地方都可通过_省略变量
4. 如果只要i下标,可写成 for i:= range numbers

   package main
   
   import "fmt"
   
   func main() {
   	//定义数组的方法
   	var arr1 [5]int
   	arr2 := [3]int{1, 3, 5}
   	arr3 := [...]int{2, 4, 6, 8, 10}
   	var grid [4][5]int
   
   	fmt.Println(arr1, arr2, arr3) //[0 0 0 0 0] [1 3 5] [2 4 6 8 10]
   	fmt.Println(grid)             //4行5列 [[0 0 0 0 0] [0 0 0 0 0] [0 0 0 0 0] [0 0 0 0 0]]
   
   	//遍历:方法一
   	/*for i:=0; i<len(arr3);i++  {
   		fmt.Println(arr3[i])
   		//2
   		//4
   		//6
   		//8
   		//10
   	}*/
   
   	//方法二
   	//下标和键值都要
   	for i,v:=range arr3 {
   		fmt.Println(i,v)
   	}
   	//0 2
   	//1 4
   	//2 6
   	//3 8
   	//4 10
   
   	//只要键值
   	for _,v:=range arr3 {
   		fmt.Println(v)
   	}
   	//2
   	//4
   	//6
   	//8
   	//10
   
   	//只要下标
   	for i := range arr3 {
   		fmt.Println(i)
   	}
   	//0
   	//1
   	//2
   	//3
   	//4
   }
   

   为什么要用range?   

•   意义明确美观
•    c++ 没有类似能力
• Java/Python:只能for each value,不能同时获取i,v

数组是值类型

• int[10] 和int[20] 是不同类型
• 调用func f(arr [10]int)会拷贝数组
• 在go语言中一般不直接使用数组

  package main
  
  import "fmt"
  
  func printArray(arr *[5]int) {
  	arr[0] = 100
  	for i, v := range arr {
  		fmt.Println(i, v)
  	}
  }
  
  func main() {
  	//定义数组的方法
  	var arr1 [5]int
  	arr2 := [3]int{1, 3, 5}
  	arr3 := [...]int{2, 4, 6, 8, 10}
  	var grid [4][5]int
  
  	fmt.Println(arr1, arr2, arr3) //[0 0 0 0 0] [1 3 5] [2 4 6 8 10]
  	fmt.Println(grid)             //4行5列 [[0 0 0 0 0] [0 0 0 0 0] [0 0 0 0 0] [0 0 0 0 0]]
  
  	//遍历:方法一
  	/*for i:=0; i<len(arr3);i++  {
  		fmt.Println(arr3[i])
  		//2
  		//4
  		//6
  		//8
  		//10
  	}*/
  
  	//方法二
  	//下标和键值都要
  	/*for i,v:=range arr3 {
  		fmt.Println(i,v)
  	}*/
  	//0 2
  	//1 4
  	//2 6
  	//3 8
  	//4 10
  
  	//只要键值
  	/*for _,v:=range arr3 {
  		fmt.Println(v)
  	}*/
  	//2
  	//4
  	//6
  	//8
  	//10
  
  	//只要下标
  	/*for i := range arr3 {
  		fmt.Println(i)
  	}*/
  	//0
  	//1
  	//2
  	//3
  	//4
  	//数组是值类型
  	fmt.Println("arr1")
  	printArray(&arr1)
  
  	fmt.Println("arr3")
  	printArray(&arr3)//取地址后
  
  	fmt.Println("arr1 and arr3")
  	fmt.Println(arr1, arr3) //取指针后  [100 0 0 0 0] [100 4 6 8 10]
  
  	//printArray(arr2)
  
  }
  

二. slice 切片:

s:=[2:6] 半开半闭区间 ,s的值为[2,3,4,5]

package main

import "fmt"

func main() {
	arr := [...]int{0,1, 2, 3, 4, 5, 6}
	s := arr[2:6]
	fmt.Println("arr[2:6]", s) //切片半开半闭区间 arr[2:6] [2 3 4 5]
}

package main

import "fmt"

func updateSlice(s []int) {
	s[0] = 100
}

func main() {
	arr := [...]int{0, 1, 2, 3, 4, 5, 6,7}
	//s := arr[2:6]
	//fmt.Println("arr[2:6]", s) //切片半开半闭区间 arr[2:6] [2 3 4 5]
	fmt.Println("arr[2:6]", arr[2:6]) // arr[开始下标:结束下标]
	fmt.Println("arr[:6]", arr[:6])
	s1 := arr[2:]
	fmt.Println("s1", arr[2:])
	s2 := arr[:]
	fmt.Println("s2", arr[:])

	fmt.Println("after update slice(s1)")
	updateSlice(s1)
	fmt.Println(s1)
	fmt.Println(arr)
	//after update slice
	//[100 33 4 5 6]
	//[0 1 100 33 4 5 6]

	fmt.Println("after update slice(s2)")
	updateSlice(s2)
	fmt.Println(s2)
	fmt.Println(arr)
	//after update slice(s2)
	//[100 1 100 33 4 5 6]
	//[100 1 100 33 4 5 6]
	fmt.Println("extending slice")
	arr[0],arr[2]=0,2
	s1=arr[2:6]
	s2=s1[3:5]
	fmt.Println("arr:",arr)//arr= [0 1 2 3 4 5 6 7]
	fmt.Println("s1:",s1)
	fmt.Println("s2:",s2)
	fmt.Println("--")
	fmt.Println("arr=",arr)
	fmt.Println("s1=%v,len(s1)=%d,cap(s1)=%d",s1,len(s1),cap(s1))//s1=%v,len(s1)=%d,cap(s1)=%d [2 3 4 5] 4 6
	fmt.Println("s2=%v,len(s2)=%d,cap(s2)=%d",s2,len(s2),cap(s2))//s2=%v,len(s2)=%d,cap(s2)=%d [5 6] 2 3
	fmt.Println(s1[3:6])// [5 6 7]
}

//arr[2:6] [2 33 4 5]
//arr[:6] [0 1 2 33 4 5]
//arr[2:] [2 33 4 5 6]
//arr[:] [0 1 2 33 4 5 6]

操作:

添加元素时如果超越cap,系统会重新分配更大的低层数组

由于值传递的关系,必须接受append的返回值

package main

import "fmt"

func printSlice(s []int) {
	fmt.Printf("%v,len=%d,cap=%d \n", s, len(s), cap(s))
}
func main() {
	fmt.Println("Create slice")
	var s []int
	for i := 0; i < 100; i++ {
		printSlice(s)
		s = append(s, 2*i+1)
	}
	fmt.Println(s)
	fmt.Println(len(s))//100

	s1 := []int{2, 4, 6, 8} [2 4 6 8],len=4,cap=4 
	s2 := make([]int, 16)//[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0],len=16,cap=16 
	s3 := make([]int, 10, 32)//[0 0 0 0 0 0 0 0 0 0],len=10,cap=32 
	printSlice(s1)
	printSlice(s2)
	printSlice(s3)

	fmt.Println("copy slice")
	copy(s2, s1)
	printSlice(s2)
	//copy slice
	//[2 4 6 8 0 0 0 0 0 0 0 0 0 0 0 0],len=16,cap=16
	
	fmt.Println("delete elements from slice")
	s2 = append(s2[:3], s2[4:]...)
	printSlice(s2)
	//delete elements from slice
	//[2 4 6 0 0 0 0 0 0 0 0 0 0 0 0],len=15,cap=16 
	
	
	fmt.Println("popping  from  front")
	front := s2[0]
	s2 = s2[1:]
	fmt.Println(front)
	printSlice(s2)
	//popping  from  front
	//2
	//[4 6 0 0 0 0 0 0 0 0 0 0 0 0],len=14,cap=15 
	
	fmt.Println("popping  from back")
	tail := s2[len(s2)-1]
	s2 = s2[:len(s2)-1]
	fmt.Println(tail)
	printSlice(s2)
	//popping  from back
	//0
	//[4 6 0 0 0 0 0 0 0 0 0 0 0],len=13,cap=15 
}

三.map

   1.map的操作

• 创建:make(map[string]int)
• 获取元素:m[key]
• key不存在时,获得value类型的初始值
• 用value,ok:=m[key]来判断是否存在key
• 用delete删除一个key

2.map的遍历

• 使用range 遍历key,或者遍历key,value对
• 不保证遍历顺序,如需顺序,需手动对key排序(借助slice)
• 使用len获得元素个数

3.map的key

• map使用哈希表,必须可以比较相等
• 除了slice,map,function的内建类型都可以作为key
• struct 类型不包含上述字段,也可作为key

package main

import "fmt"

func main() {
	//定义map3种方式
	m := map[string]string{
		"name":    "lxw",
		"course":  "golang",
		"site":    "imooc",
		"quality": "notbad",
	}
	m2 := make(map[string]int) //m2==empty map

	var m3 map[string]int //m3==nil

	fmt.Println(m, m2, m3)
	fmt.Println("==traversing map==")
	for k, v := range m {
		fmt.Println(k, v)
	}

	fmt.Println("---getting values---")
	courseName, ok := m["course"]
	fmt.Println(courseName, ok)

	//判断键是否存在
	if casseName, ok2 := m["caurse"]; ok2 {
		fmt.Println(casseName)
	} else {
		fmt.Println("key does not exist")
	}

	fmt.Println("--deleting values---")
	courseName, ok3 := m["name"]
	fmt.Println(courseName, ok3)

	delete(m, "name")
	courseName, ok3 = m["name"]
	fmt.Println(courseName, ok3)
}
/*map[course:golang name:lxw quality:notbad site:imooc] map[] map[]
==traversing map==
quality notbad
name lxw
course golang
site imooc
---getting values---
golang true
key does not exist
--deleting values---
lxw true
false*/

package main

import "fmt"
//最长不含有重复字符的子串
func lenthOfNonRepeatingSubstr(s string) int {
	lastOccurred := make(map[byte]int)
	start := 0
	maxLength := 0
	for i, ch := range []byte(s) {
		if lastI, ok := lastOccurred[ch]; ok && lastI >= start {
			start = lastI + 1
		}
		if i-start+1 > maxLength {
			maxLength = i - start + 1
		}
		lastOccurred[ch] = i
	}
	return maxLength
}

func main() {
	fmt.Println(lenthOfNonRepeatingSubstr("abcabcbb")) //3
	fmt.Println(lenthOfNonRepeatingSubstr("bbbbb"))    //1
	fmt.Println(lenthOfNonRepeatingSubstr("pwwkew"))   //3
}

四.字符串

• rune 相当于go的char;每个中文3个字节;
• 使用range遍历pos,rune对
• 使用utf8.RuneCountInString获得字符数量
• 使用len获得字节长度
• 使用[]byte获得字节

其他字符串操作

• Fileds,split,join
• Contains,Index
• Tolower,toupper
• Trim,trimRight,trimLeft

  //最长不含有重复字符的子串(国际版中英文都可以)
  package main
  
  import "fmt"
  //最长不含有重复字符的子串
  func lenthOfNonRepeatingSubstr(s string) int {
  	lastOccurred := make(map[rune]int)
  	start := 0
  	maxLength := 0
  	for i, ch := range []rune(s) {
  		if lastI, ok := lastOccurred[ch]; ok && lastI >= start {
  			start = lastI + 1
  		}
  		if i-start+1 > maxLength {
  			maxLength = i - start + 1
  		}
  		lastOccurred[ch] = i
  	}
  	return maxLength
  }
  
  func main() {
  	fmt.Println(lenthOfNonRepeatingSubstr("abcabcbb")) //3
  	fmt.Println(lenthOfNonRepeatingSubstr("bbbbb"))    //1
  	fmt.Println(lenthOfNonRepeatingSubstr("pwwkew"))   //3
  	fmt.Println(lenthOfNonRepeatingSubstr(""))//0
  	fmt.Println(lenthOfNonRepeatingSubstr("b"))//1
  	fmt.Println(lenthOfNonRepeatingSubstr("abcdef"))//6
  	fmt.Println(lenthOfNonRepeatingSubstr("这里是中国"))//5
  	fmt.Println(lenthOfNonRepeatingSubstr("一二三二一"))//3
  	fmt.Println(lenthOfNonRepeatingSubstr("黑化肥发灰会挥发灰化肥发挥会发黑"))//7
  }