81 lines
1.7 KiB
Go
81 lines
1.7 KiB
Go
package containers
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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 Stack[T any] struct {
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top *ChainElem[T]
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bottom *ChainElem[T]
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}
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// isValid checks if the stack is valid.
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func (s *Stack[T]) isValid() bool {
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return s.top != nil &&
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s.bottom != nil &&
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reachable(s.top, s.bottom)
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}
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// IsEmpty checks if the stack is currently empty.
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func (s *Stack[T]) IsEmpty() bool {
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return s.top == s.bottom
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}
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// Push adds a new element to the top of the stack.
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// It errors out if the stack is invalid.
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func (s *Stack[T]) Push(e *T) error {
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if !s.isValid() {
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return errors.New("stack invalid")
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}
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n := emptyElem[T]()
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n.Elem = e
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n.Next = s.top
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s.top = n
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return nil
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}
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// Pop removes the first element at the top of the stack and returns it.
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// It errors out if the stack is invalid or empty.
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func (s *Stack[T]) Pop() (*T, error) {
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if !s.isValid() {
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return nil, errors.New("stack invalid")
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}
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if s.IsEmpty() {
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return nil, errors.New("stack empty")
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}
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e := s.top.Elem
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s.top = s.top.Next
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return e, nil
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}
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// Top returns the first element at the top of the stack without removing it.
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// It errors out if the stack is empty or invalid.
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func (s *Stack[T]) Top() (*T, error) {
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if !s.isValid() {
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return nil, errors.New("stack invalid")
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}
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if s.IsEmpty() {
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return nil, errors.New("stack empty")
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}
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return s.top.Elem, nil
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}
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// MarshalJSON is used by json.Marshal to create a json representation.
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func (s *Stack[T]) MarshalJSON() ([]byte, error) {
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if !s.isValid() {
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return nil, errors.New("queue invalid")
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}
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if s.IsEmpty() {
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return nil, errors.New("queue empty")
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}
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return json.Marshal(s.top)
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}
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func BuildStack[T any]() *Stack[T] {
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empty := emptyElem[T]()
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return &Stack[T]{
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top: empty,
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bottom: empty,
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}
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}
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