Quick implementation of a Queue (and Stack) using a double linked listed under the hood in go

double-linked-list.go

type doubleLinkedList struct {
    head *linkedNode
    tail *linkedNode
    size int
}

type linkedNode struct {
    val  int
    next *linkedNode
    prev *linkedNode
}

func (q *doubleLinkedList) enqueue(val int) {
    n := &linkedNode{val: val, next: nil, prev: nil}
    
    if q.size == 0 {
        q.head = n
        
    } else if q.size == 1 {
        n.prev = q.head
        q.head.next = n
        q.tail = n
        
    } else {
        n.prev = q.tail
        q.tail.next = n
        q.tail = n
    }
    
    q.size++
}

func (q *doubleLinkedList) dequeue() int {
    first := q.head
    q.head = q.head.next
    q.size--
    return first.val
}

func (q *doubleLinkedList) pop() int {
    var last *linkedNode
    
    // 1
    if q.size == 1 {
        last = q.head
        q.head = nil
        q.tail = nil
        
    // 1, 2
    } else if q.size == 2 {
        last = q.tail
        q.tail = nil
        
   // 1, 2, 3
    } else {
        last = q.tail
        q.tail = last.prev
    }

    q.size--
    return last.val
}

func (q *doubleLinkedList) last() int {
    if q.size == 1 {
        return q.first()
    }
    
    return q.tail.val
}


func (q *doubleLinkedList) first() int {
    return q.head.val
}