155 lines
2.6 KiB
Go
155 lines
2.6 KiB
Go
package maps
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// list is a doubly-linked list containing elemnts with key-value pairs of given generic parameter types.
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type list[K comparable, V any] struct {
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head *elem[K, V]
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tail *elem[K, V]
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len int
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}
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// Index returns the element at index from list.
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func (l *list[K, V]) Index(idx int) *elem[K, V] {
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switch {
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// Idx in first half
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case idx < l.len/2:
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elem := l.head
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for i := 0; i < idx; i++ {
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elem = elem.next
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}
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return elem
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// Index in last half
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default:
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elem := l.tail
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for i := l.len - 1; i > idx; i-- {
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elem = elem.prev
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}
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return elem
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}
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}
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// PushFront will push the given element to the front of the list.
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func (l *list[K, V]) PushFront(elem *elem[K, V]) {
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if l.len == 0 {
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// Set new tail + head
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l.head = elem
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l.tail = elem
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// Link elem to itself
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elem.next = elem
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elem.prev = elem
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} else {
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oldHead := l.head
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// Link to old head
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elem.next = oldHead
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oldHead.prev = elem
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// Link up to tail
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elem.prev = l.tail
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l.tail.next = elem
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// Set new head
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l.head = elem
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}
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// Incr count
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l.len++
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}
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// PushBack will push the given element to the back of the list.
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func (l *list[K, V]) PushBack(elem *elem[K, V]) {
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if l.len == 0 {
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// Set new tail + head
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l.head = elem
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l.tail = elem
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// Link elem to itself
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elem.next = elem
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elem.prev = elem
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} else {
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oldTail := l.tail
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// Link up to head
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elem.next = l.head
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l.head.prev = elem
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// Link to old tail
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elem.prev = oldTail
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oldTail.next = elem
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// Set new tail
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l.tail = elem
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}
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// Incr count
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l.len++
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}
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// PopTail will pop the current tail of the list, returns nil if empty.
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func (l *list[K, V]) PopTail() *elem[K, V] {
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if l.len == 0 {
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return nil
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}
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elem := l.tail
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l.Unlink(elem)
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return elem
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}
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// Unlink will unlink the given element from the doubly-linked list chain.
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func (l *list[K, V]) Unlink(elem *elem[K, V]) {
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if l.len <= 1 {
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// Drop elem's links
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elem.next = nil
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elem.prev = nil
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// Only elem in list
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l.head = nil
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l.tail = nil
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l.len = 0
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return
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}
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// Get surrounding elems
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next := elem.next
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prev := elem.prev
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// Relink chain
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next.prev = prev
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prev.next = next
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switch elem {
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// Set new head
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case l.head:
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l.head = next
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// Set new tail
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case l.tail:
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l.tail = prev
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}
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// Drop elem's links
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elem.next = nil
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elem.prev = nil
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// Decr count
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l.len--
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}
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// elem represents an element in a doubly-linked list.
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type elem[K comparable, V any] struct {
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next *elem[K, V]
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prev *elem[K, V]
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K K
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V V
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}
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// allocElems will allocate a slice of empty elements of length.
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func allocElems[K comparable, V any](i int) []*elem[K, V] {
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s := make([]*elem[K, V], i)
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for i := range s {
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s[i] = &elem[K, V]{}
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}
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return s
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}
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