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package list
// Elem represents an element in a doubly-linked list.
type Elem[T any] struct {
Next *Elem[T]
Prev *Elem[T]
Value T
}
// List implements a doubly-linked list, where:
// - Head = index 0 (i.e. the front)
// - Tail = index n-1 (i.e. the back)
type List[T any] struct {
Head *Elem[T]
Tail *Elem[T]
len int
}
// Len returns the current list length.
func (l *List[T]) Len() int {
return l.len
}
// PushFront adds 'v' to the beginning of the list.
func (l *List[T]) PushFront(v T) *Elem[T] {
elem := &Elem[T]{Value: v}
l.PushElemFront(elem)
return elem
}
// PushBack adds 'v' to the end of the list.
func (l *List[T]) PushBack(v T) *Elem[T] {
elem := &Elem[T]{Value: v}
l.PushElemBack(elem)
return elem
}
// InsertBefore adds 'v' into the list before 'at'.
func (l *List[T]) InsertBefore(v T, at *Elem[T]) *Elem[T] {
elem := &Elem[T]{Value: v}
l.InsertElemBefore(elem, at)
return elem
}
// InsertAfter adds 'v' into the list after 'at'.
func (l *List[T]) InsertAfter(v T, at *Elem[T]) *Elem[T] {
elem := &Elem[T]{Value: v}
l.InsertElemAfter(elem, at)
return elem
}
// PushFrontNode adds 'elem' to the front of the list.
func (l *List[T]) PushElemFront(elem *Elem[T]) {
if elem == l.Head {
return
}
// Set new head.
oldHead := l.Head
l.Head = elem
if oldHead != nil {
// Link to old head
elem.Next = oldHead
oldHead.Prev = elem
} else {
// First in list.
l.Tail = elem
}
// Incr count
l.len++
}
// PushBackNode adds 'elem' to the back of the list.
func (l *List[T]) PushElemBack(elem *Elem[T]) {
if elem == l.Tail {
return
}
// Set new tail.
oldTail := l.Tail
l.Tail = elem
if oldTail != nil {
// Link to old tail
elem.Prev = oldTail
oldTail.Next = elem
} else {
// First in list.
l.Head = elem
}
// Incr count
l.len++
}
// InsertElemAfter adds 'elem' into the list after 'at' (i.e. at.Next = elem).
func (l *List[T]) InsertElemAfter(elem *Elem[T], at *Elem[T]) {
if elem == at {
return
}
// Set new 'next'.
oldNext := at.Next
at.Next = elem
// Link to 'at'.
elem.Prev = at
if oldNext == nil {
// Set new tail
l.Tail = elem
} else {
// Link to 'prev'.
oldNext.Prev = elem
elem.Next = oldNext
}
// Incr count
l.len++
}
// InsertElemBefore adds 'elem' into the list before 'at' (i.e. at.Prev = elem).
func (l *List[T]) InsertElemBefore(elem *Elem[T], at *Elem[T]) {
if elem == at {
return
}
// Set new 'prev'.
oldPrev := at.Prev
at.Prev = elem
// Link to 'at'.
elem.Next = at
if oldPrev == nil {
// Set new head
l.Head = elem
} else {
// Link to 'next'.
oldPrev.Next = elem
elem.Prev = oldPrev
}
// Incr count
l.len++
}
// Remove removes the 'elem' from the list.
func (l *List[T]) Remove(elem *Elem[T]) {
// Get linked elems.
next := elem.Next
prev := elem.Prev
// Unset elem.
elem.Next = nil
elem.Prev = nil
switch {
// elem is ONLY one in list.
case next == nil && prev == nil:
l.Head = nil
l.Tail = nil
// elem is front in list.
case next != nil && prev == nil:
l.Head = next
next.Prev = nil
// elem is last in list.
case prev != nil && next == nil:
l.Tail = prev
prev.Next = nil
// elem in middle of list.
default:
next.Prev = prev
prev.Next = next
}
// Decr count
l.len--
}
// Range calls 'fn' on every element from head forward in list.
func (l *List[T]) Range(fn func(*Elem[T])) {
if fn == nil {
panic("nil function")
}
for elem := l.Head; elem != nil; elem = elem.Next {
fn(elem)
}
}
// RangeReverse calls 'fn' on every element from tail backward in list.
func (l *List[T]) RangeReverse(fn func(*Elem[T])) {
if fn == nil {
panic("nil function")
}
for elem := l.Tail; elem != nil; elem = elem.Prev {
fn(elem)
}
}
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