95 lines
2 KiB
Go
95 lines
2 KiB
Go
package datastructs
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import (
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"encoding/json"
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"errors"
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)
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type Queue[T any] struct {
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head *ChainElem[T]
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tail *ChainElem[T]
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}
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// isValid checks if the queue is still valid.
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func (q *Queue[T]) isValid() bool {
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return q.head != nil &&
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q.tail != nil &&
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reachable(q.head, q.tail)
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}
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// IsEmpty checks if the queue is empty.
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func (q *Queue[T]) IsEmpty() bool {
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return q.head == q.tail
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}
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// Push adds a new element to the end of the queue.
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func (q *Queue[T]) Push(elem *T) error {
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if !q.isValid() {
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return errors.New("invalid queue")
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}
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e := emptyElem[T]()
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q.tail.Elem = elem
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q.tail.Next = e
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q.tail = e
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return nil
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}
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// Pop removes the first element of the queue.
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// It errors out if there is no element or the queue is invalid.
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func (q *Queue[T]) Pop() (*T, error) {
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if !q.isValid() {
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return nil, errors.New("invalid queue")
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}
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if q.IsEmpty() {
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return nil, errors.New("empty queue")
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}
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Elem := q.head.Elem
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q.head = q.head.Next
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return Elem, nil
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}
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// Top returns the first element of the queue without removing it.
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// It errors out if there is no element or the queue is invalid.
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func (q *Queue[T]) Top() (*T, error) {
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if !q.isValid() {
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return nil, errors.New("queue invalid")
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}
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if q.IsEmpty() {
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return nil, errors.New("queue empty")
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}
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return q.head.Elem, nil
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}
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// HeadElem returns the first ChainElem of the queue without removing it.
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// It errors out if there is no element or the queue is invalid.
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func (q *Queue[T]) HeadElem() (*ChainElem[T], error) {
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if !q.isValid() {
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return nil, errors.New("queue invalid")
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}
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if q.IsEmpty() {
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return nil, errors.New("queue empty")
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}
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return q.head, nil
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}
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// MarshalJSON is used for generating json data when using json.Marshal.
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func (q *Queue[T]) MarshalJSON() ([]byte, error) {
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if !q.isValid() {
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return nil, errors.New("queue invalid")
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}
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if q.IsEmpty() {
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return nil, errors.New("queue empty")
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}
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return json.Marshal(q.head)
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}
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func BuildQueue[T any]() *Queue[T] {
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empty := emptyElem[T]()
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return &Queue[T]{
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head: empty,
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tail: empty,
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}
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}
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