如何在Golang中的列表中构造循环

Question

I wrote a function to find the loop in a list using golang. But I am not able to construct a loop in a list as input.

Please find below the code,

package main
    import (
        "container/list"
        "fmt"
    )
    func main() {
        l := list.New()
        l.PushBack(0)
        l.PushBack(1)
        l.PushBack(2)
        l.PushBack(3)
        l.PushBack(4)
        l.PushBack(5)

        e6 := l.PushBack(6)
        l.PushBack(7)
        e8 :=l.PushBack(8)
        e9 := l.InsertAfter(9,e8)
        l.InsertBefore(e9, e6)

        for e:=l.Front() ; e !=nil ; e=e.Next() {
            fmt.Println(e.Value)
        }
    }

could anyone help me on this?

Answer 1

It is not possible to construct a loop using the container/list List type. The List type methods ensure that there's no loop. Because the list Element's next and previous pointers are not exported, the application cannot create a loop by modifying the elements directly.

You can define your own type to create a list with a loop:

package main

import "fmt"

type node struct {
    v    int
    next *node
}

func main() {
    // Create list with 1, 2, 3 and print.

    l := &node{1, &node{2, &node{3, nil}}}
    for n := l; n != nil; n = n.next {
        fmt.Println(n.v)
    }

    // Create list with loop and print at most 100 steps down the list.

    n3 := &node{3, nil}
    l = &node{1, &node{2, n3}}
    n3.next = l

    for i, n := 0, l; n != nil && i < 100; n, i = n.next, i+1 {
        fmt.Println(n.v)
    }

}

playground example