[Golang] Container / ring source code analysis

I was going to look at the heap first and found that sort was referenced. Wait, let's watch ring first, then sort.

First look at the data structure:

type Ring struct {
	next, prev *Ring
	Value      interface{} // for use by client; untouched by this library
}

Simple, much like a linked list. ring.

Simple initialization:

func (r *Ring) init() *Ring {
	r.next = r
	r.prev = r
	return r
}

The iterative function is also relatively simple:

func (r *Ring) Next() *Ring {
	if r.next == nil {
		return r.init()
	}
	return r.next
}

func (r *Ring) Prev() *Ring {
	if r.next == nil {
		return r.init()
	}
	return r.prev
}

Move move function, less than 0 forward, greater than 0 backward:

func (r *Ring) Move(n int) *Ring {
	if r.next == nil {
		return r.init()
	}
	switch {
	case n < 0:
		for ; n < 0; n++ {
			r = r.prev
		}
	case n > 0:
		for ; n > 0; n-- {
			r = r.next
		}
	}
	return n
}

Create n elements:

func New(n int) *Ring {
	if n <= 0 {
		return nil
	}
	r := new(Ring)
	p := r
	for i := 1; i < n; i++ {
		p.next = &Ring{prev: p}
		p = p.next
	}
	p.next = r
	r.prev = p
	return r
}

link和unlink：

func (r *Ring) Link(s *Ring) *Ring {
	n := r.Next()
	if s != nil {
		p := s.Prev()
		// Note: Cannot use multiple assignment because
		// evaluation order of LHS is not specified.
		r.next = s
		s.prev = r
		n.prev = p
		p.next = n
	}
	return n
}

func (r *Ring) Unlink(n int) *Ring {
	if n <= 0 {
		return nil
	}
	return r.Link(r.Move(n + 1))
}

Note that unlink uses link.

Calculate the length of the ring:

func (r *Ring) Len() int {
	n := 0
	if r != nil {
		n = 1
		for p := r.Next(); p != r; p = p.next {
			n++
		}
	}
	return n
}

Time complexity is n

A little special is this do function, which calls the specified func for each element in the ring:

func (r *Ring) Do(f func(interface{})) {
	if r != nil {
		f(r.Value)
		for p := r.Next(); p != r; p = p.next {
			f(p.Value)
		}
	}
}