// demonstration of doubly linked list in golang⏎
⏎
package doublelinkedlist⏎
⏎
// package main⏎
⏎
import "fmt"⏎
⏎
type node struct {⏎
	val  int⏎
	next *node⏎
	prev *node⏎
}⏎
⏎
type doublelinkedlist struct {⏎
	head *node⏎
}⏎
⏎
// to avoid mistakes when using pointer vs struct for new node creation⏎
func newNode(val int) *node {⏎
	n := &node{}⏎
	n.val = val⏎
	n.next = nil⏎
	n.prev = nil⏎
	return n⏎
}⏎
⏎
func (ll *doublelinkedlist) addAtBeg(val int) {⏎
	n := newNode(val)⏎
	n.next = ll.head⏎
	ll.head = n⏎
}⏎
⏎
func (ll *doublelinkedlist) addAtEnd(val int) {⏎
	n := newNode(val)⏎
⏎
	if ll.head == nil {⏎
		ll.head = n⏎
		return⏎
	}⏎
⏎
	cur := ll.head⏎
	for ; cur.next != nil; cur = cur.next {⏎
	}⏎
	cur.next = n⏎
	n.prev = cur⏎
}⏎
⏎
func (ll *doublelinkedlist) delAtBeg() int {⏎
	if ll.head == nil {⏎
		return -1⏎
	}⏎
⏎
	cur := ll.head⏎
	ll.head = cur.next⏎
⏎
	if ll.head != nil {⏎
		ll.head.prev = nil⏎
	}⏎
⏎
	return cur.val⏎
}⏎
⏎
func (ll *doublelinkedlist) delAtEnd() int {⏎
	// no item⏎
	if ll.head == nil {⏎
		return -1⏎
	}⏎
⏎
	// only one item⏎
	if ll.head.next == nil {⏎
		return ll.delAtBeg()⏎
	}⏎
⏎
	// more than one, go to second last⏎
	cur := ll.head⏎
	for ; cur.next.next != nil; cur = cur.next {⏎
	}⏎
⏎
	retval := cur.next.val⏎
	cur.next = nil⏎
	return retval⏎
}⏎
⏎
func (ll *doublelinkedlist) count() int {⏎
	var ctr int = 0⏎
⏎
	for cur := ll.head; cur != nil; cur = cur.next {⏎
		ctr += 1⏎
	}⏎
⏎
	return ctr⏎
}⏎
⏎
func (ll *doublelinkedlist) reverse() {⏎
	var prev, next *node⏎
	cur := ll.head⏎
⏎
	for cur != nil {⏎
		next = cur.next⏎
		cur.next = prev⏎
		cur.prev = next⏎
		prev = cur⏎
		cur = next⏎
	}⏎
⏎
	ll.head = prev⏎
}⏎
⏎
func (ll *doublelinkedlist) display() {⏎
	for cur := ll.head; cur != nil; cur = cur.next {⏎
		fmt.Print(cur.val, " ")⏎
	}⏎
⏎
	fmt.Print("\n")⏎
}⏎
⏎
func (ll *doublelinkedlist) displayReverse() {⏎
	if ll.head == nil {⏎
		return⏎
	}⏎
	var cur *node⏎
	for cur = ll.head; cur.next != nil; cur = cur.next {⏎
	}⏎
⏎
	for ; cur != nil; cur = cur.prev {⏎
		fmt.Print(cur.val, " ")⏎
	}⏎
⏎
	fmt.Print("\n")⏎
}⏎
⏎
/*⏎
func main() {⏎
	ll := doublelinkedlist{}⏎
⏎
	ll.addAtBeg(10)⏎
	ll.addAtEnd(20)⏎
	ll.display()⏎
	ll.addAtBeg(30)⏎
	ll.display()⏎
⏎
	ll.reverse()⏎
	ll.display()⏎
	ll.displayReverse()⏎
⏎
	fmt.Print(ll.delAtBeg(), "\n")⏎
	fmt.Print(ll.delAtEnd(), "\n")⏎
	fmt.Print("Display")⏎
	ll.display()⏎
	fmt.Print(ll.delAtBeg(), "\n")⏎
	ll.display()⏎
	fmt.Print(ll.delAtBeg(), "\n")⏎
	ll.display()⏎
}⏎
*/⏎