Data structure: Stack (2)

Adjust the single linked list and stack interface based on the previous implementation. Move the size variable to the list.

type Stack struct {
	list *SinglyLinkedList
}

func NewStack(a) *Stack {
	return &Stack{
		list: &SinglyLinkedList{},
	}
}

func (o *Stack) Len(a) int {
	return o.list.Len()
}

func (o *Stack) IsEmpty(a) bool {
	return o.list.Len() == 0
}

func (o *Stack) Push(v interface{}) {
	o.list.AddToHead(v)
}

func (o *Stack) Peek(a) interface{} {
	if o.IsEmpty() {
		panic("Stack is empty")}return o.list.Head().V
}

func (o *Stack) Pop(a) {
	if o.IsEmpty() {
		panic("Stack is empty")
	}
	o.list.RemoveHead()
}

// Single linked list node
type SLLNode struct {
	V interface{}
	Next *SLLNode
}

/ / singly linked lists
type SinglyLinkedList struct {
	head *SLLNode
        size int
}

func (o *SinglyLinkedList) Len(a) int {
        return o.size
}

func (o *SinglyLinkedList) AddToHead(v interface{}) {
	o.head = &SLLNode{
		V: v,
                Next: o.head,
	}
        o.size++
}

func (o *SinglyLinkedList) Head(a) *SLLNode {
	return o.head
}

func (o *SinglyLinkedList) RemoveHead(a) {
	if o.head == nil {
		panic("SinglyLinkedList. head is nil")
	}
	o.head = o.head.Next
        o.size--
}
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