Go -- standard library sort package

sort There are many functions in the package , More commonly used are Sort function 、IsSorted function 、Slice function 、Search function .

 
To use sort Package functions , Need to achieve sort.Interface, Including the following 3 A way

type Interface interface {
    
        Len() int            //  Returns the current number of elements 
        Less(i, j int) bool. //  Judgment No. i The first element is less than the j Elements 
        Swap(i, j int)       //  Exchange two elements 
}

  sort The package has implemented several common base types （int,float,string and slice） Of sort.Interface The method in , We can use it directly .
 

1、Sort function

  Sort The function is used to specify Interface Sort

 
Yes int Type array

func main()  {
    
	a := []int{
    1, 2, 5, 3, 4}
	sort.Ints(a)
	fmt.Println(a)
}

Yes float64 Type slice

func main()  {
    
	a := []float64{
    1, 2.9, 0.5, 3, 4}
	sort.Float64s(a)
	fmt.Println(a)
}

 

2、IsSorted function

  IsSorted The function is used to determine whether it is ordered
 
Judge int Type of the array

func main()  {
    
	a := []int{
    1, 2, 5, 3, 4}
	fmt.Println(sort.IntsAreSorted(a))
	sort.Ints(a)
	fmt.Println(a)
	fmt.Println(sort.IntsAreSorted(a))
}

 

3、Slice function

  Slice The function is used to evaluate a Slice Sort , Function takes two parameters , The first one needs to be sorted Slice, The second is Slice Element comparison function . Two dimensional slices can be compared .
 
Sort by the first column

func main() {
    
	interval := [][]int{
    
		{
    2,3},
		{
    1,3},
		{
    2,4},
		{
    2,2},
	}
	sort.Slice(interval, func(i, j int) bool {
    
		return interval[i][0] < interval[j][0]
	})
	fmt.Println(interval)
}

The first column is the same , Sort by the second column

func main() {
    
	interval := [][]int{
    
		{
    2,3},
		{
    1,3},
		{
    2,4},
		{
    2,2},
	}
	sort.Slice(interval, func(i, j int) bool {
    
		if  interval[i][0] ==  interval[j][0] {
    
			return interval[i][1] < interval[j][1]
		}else {
    
			return interval[i][0] <  interval[j][0]
		}
	})
	fmt.Println(interval)
}

  

4、Search function

   Used to binary find the position of the specified element .
 
lookup int The position of the specified element in the array

func main()  {
    
	a := []int{
    1, 2, 5, 3, 4}
	fmt.Println(sort.SearchInts(a,3))
	sort.Ints(a)
	fmt.Println(sort.SearchInts(a,3))
}

output:

2
2

As can be seen from the output , Whatever comes in a Is it orderly , All of them 3 stay Orderly a Position in .

 

5、 Other types

   The above examples have been implemented by the government Len()、Less()、Swap() Methodical , If it is any other structure that we customize , We need to implement three methods before we can use sort Related functions in the package .
 
such as :

type Person struct {
    
	Name string
	Age int
}
type Persons []Person

func (p Persons) Len() int           {
     return len(p) }
func (p Persons) Less(i, j int) bool {
     return p[i].Age < p[j].Age }   // Sort by age 
func (p Persons) Swap(i, j int)      {
     p[i], p[j] = p[j], p[i] }

func main()  {
    
	p1:=Person{
    "a",3}
	p2:=Person{
    "b",7}
	p3:=Person{
    "c",5}
	p :=Persons{
    p1,p2,p3}
	fmt.Println(p)
	fmt.Println(sort.IsSorted(p))   // At this time, disorder , return false
	sort.Sort(p)
	fmt.Println(p)
	fmt.Println(sort.IsSorted(p))   // It's in order , return true
}