Add solution for Challenge 27 by Johrespi (#723)

* Add solution for Challenge 27

* Update challenge-27/submissions/Johrespi/solution-template.go

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

---------

Co-authored-by: go-interview-practice-bot[bot] <230190823+go-interview-practice-bot[bot]@users.noreply.github.com>
Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: 3 people

challenge-27/submissions/Johrespi/solution-template.go

@@ -0,0 +1,355 @@
+package generics
+
+import "errors"
+
+// ErrEmptyCollection is returned when an operation cannot be performed on an empty collection
+var ErrEmptyCollection = errors.New("collection is empty")
+
+//
+// 1. Generic Pair
+//
+
+// Pair represents a generic pair of values of potentially different types
+type Pair[T, U any] struct {
+	First  T
+	Second U
+}
+
+// NewPair creates a new pair with the given values
+func NewPair[T, U any](first T, second U) Pair[T, U] {
+	// TODO: Implement this function
+	return Pair[T, U]{First: first, Second: second}
+}
+
+// Swap returns a new pair with the elements swapped
+func (p Pair[T, U]) Swap() Pair[U, T] {
+	// TODO: Implement this method
+	return Pair[U, T]{First: p.Second, Second: p.First}
+}
+
+//
+// 2. Generic Stack
+//
+
+// Stack is a generic Last-In-First-Out (LIFO) data structure
+type Stack[T any] struct {
+	// TODO: Add necessary fields
+	items []T
+}
+
+// NewStack creates a new empty stack
+func NewStack[T any]() *Stack[T] {
+	// TODO: Implement this function
+	return &Stack[T]{items: []T{}}
+}
+
+// Push adds an element to the top of the stack
+func (s *Stack[T]) Push(value T) {
+	// TODO: Implement this method
+	s.items = append(s.items, value)
+}
+
+// Pop removes and returns the top element from the stack
+// Returns an error if the stack is empty
+func (s *Stack[T]) Pop() (T, error) {
+	// TODO: Implement this method
+
+	if len(s.items) == 0 {
+		var zero T
+		return zero, ErrEmptyCollection
+	}
+
+	var removed T
+	removed = s.items[len(s.items)-1]
+	s.items = s.items[:len(s.items)-1] // [5,8,9]
+	return removed, nil
+}
+
+// Peek returns the top element without removing it
+// Returns an error if the stack is empty
+func (s *Stack[T]) Peek() (T, error) {
+	// TODO: Implement this method
+	if len(s.items) == 0 {
+		var zero T
+		return zero, ErrEmptyCollection
+	}
+
+	top := s.items[len(s.items)-1]
+	return top, nil
+}
+
+// Size returns the number of elements in the stack
+func (s *Stack[T]) Size() int {
+	// TODO: Implement this method
+	return len(s.items)
+}
+
+// IsEmpty returns true if the stack contains no elements
+func (s *Stack[T]) IsEmpty() bool {
+	// TODO: Implement this method
+
+	if len(s.items) == 0 {
+		return true
+	}
+
+	return false
+}
+
+//
+// 3. Generic Queue
+//
+
+// Queue is a generic First-In-First-Out (FIFO) data structure
+type Queue[T any] struct {
+	// TODO: Add necessary fields
+	items []T
+}
+
+// NewQueue creates a new empty queue
+func NewQueue[T any]() *Queue[T] {
+	// TODO: Implement this function
+	return &Queue[T]{items: []T{}}
+}
+
+// Enqueue adds an element to the end of the queue
+func (q *Queue[T]) Enqueue(value T) {
+	// TODO: Implement this method
+	q.items = append(q.items, value)
+}
+
+// Dequeue removes and returns the front element from the queue
+// Returns an error if the queue is empty
+func (q *Queue[T]) Dequeue() (T, error) {
+	// TODO: Implement this method
+	var zero T
+
+	if len(q.items) == 0 {
+		return zero, ErrEmptyCollection
+	}
+
+	removed := q.items[0]
+	q.items = q.items[1:]
+
+	return removed, nil
+}
+
+// Front returns the front element without removing it
+// Returns an error if the queue is empty
+func (q *Queue[T]) Front() (T, error) {
+	// TODO: Implement this method
+	var zero T
+
+	if len(q.items) == 0 {
+		return zero, ErrEmptyCollection
+	}
+
+	front := q.items[0]
+	return front, nil
+}
+
+// Size returns the number of elements in the queue
+func (q *Queue[T]) Size() int {
+	// TODO: Implement this method
+	return len(q.items)
+}
+
+// IsEmpty returns true if the queue contains no elements
+func (q *Queue[T]) IsEmpty() bool {
+	// TODO: Implement this method
+	if len(q.items) == 0 {
+		return true
+	}
+	return false
+}
+
+//
+// 4. Generic Set
+//
+
+// Set is a generic collection of unique elements
+type Set[T comparable] struct {
+	// TODO: Add necessary fields
+	items map[T]bool
+}
+
+// NewSet creates a new empty set
+func NewSet[T comparable]() *Set[T] {
+	// TODO: Implement this function
+	return &Set[T]{items: map[T]bool{}}
+}
+
+// Add adds an element to the set if it's not already present
+func (s *Set[T]) Add(value T) {
+	// TODO: Implement this method
+	if s.items == nil {
+		s.items = make(map[T]bool)
+	}
+	s.items[value] = true
+}
+
+// Remove removes an element from the set if it exists
+func (s *Set[T]) Remove(value T) {
+	// TODO: Implement this method
+	delete(s.items, value)
+}
+
+// Contains returns true if the set contains the given element
+func (s *Set[T]) Contains(value T) bool {
+	// TODO: Implement this method
+	_, exists := s.items[value]
+	if exists {
+		return true
+	}
+	return false
+}
+
+// Size returns the number of elements in the set
+func (s *Set[T]) Size() int {
+	// TODO: Implement this method
+	return len(s.items)
+}
+
+// Elements returns a slice containing all elements in the set
+func (s *Set[T]) Elements() []T {
+	// TODO: Implement this method
+
+	if len(s.items) == 0 {
+		return []T{}
+	}
+
+	var res []T
+	for k, _ := range s.items {
+		res = append(res, k)
+	}
+
+	return res
+}
+
+// Union returns a new set containing all elements from both sets
+func Union[T comparable](s1, s2 *Set[T]) *Set[T] {
+	// TODO: Implement this function
+
+	s3 := NewSet[T]()
+
+	for k, _ := range s1.items {
+		s3.Add(k)
+	}
+
+	for k, _ := range s2.items {
+		s3.Add(k)
+	}
+
+	return s3
+}
+
+// Intersection returns a new set containing only elements that exist in both sets
+func Intersection[T comparable](s1, s2 *Set[T]) *Set[T] {
+	// TODO: Implement this function
+
+	s3 := NewSet[T]()
+
+	for k, _ := range s1.items {
+		if s2.Contains(k) {
+			s3.Add(k)
+		}
+	}
+
+	return s3
+}
+
+// Difference returns a new set with elements in s1 that are not in s2
+func Difference[T comparable](s1, s2 *Set[T]) *Set[T] {
+	// TODO: Implement this function
+
+	s3 := NewSet[T]()
+
+	for k, _ := range s1.items {
+		if !s2.Contains(k) {
+			s3.Add(k)
+		}
+	}
+	return s3
+}
+
+//
+// 5. Generic Utility Functions
+//
+
+// Filter returns a new slice containing only the elements for which the predicate returns true
+func Filter[T any](slice []T, predicate func(T) bool) []T {
+	// TODO: Implement this function
+
+	var res []T
+	for _, v := range slice {
+		if predicate(v) {
+			res = append(res, v)
+		}
+	}
+	return res
+}
+
+// Map applies a function to each element in a slice and returns a new slice with the results
+func Map[T, U any](slice []T, mapper func(T) U) []U {
+	// TODO: Implement this function
+
+	var res []U
+	for _, v := range slice {
+		res = append(res, mapper(v))
+	}
+	return res
+}
+
+// Reduce reduces a slice to a single value by applying a function to each element
+func Reduce[T, U any](slice []T, initial U, reducer func(U, T) U) U {
+	// TODO: Implement this function
+
+	for _, v := range slice {
+		initial = reducer(initial, v)
+	}
+
+	return initial
+}
+
+// Contains returns true if the slice contains the given element
+func Contains[T comparable](slice []T, element T) bool {
+	// TODO: Implement this function
+
+	for _, e := range slice {
+		if e == element {
+			return true
+		}
+	}
+
+	return false
+}
+
+// FindIndex returns the index of the first occurrence of the given element or -1 if not found
+func FindIndex[T comparable](slice []T, element T) int {
+	// TODO: Implement this function
+
+	for i, e := range slice {
+		if e == element {
+			return i
+		}
+	}
+
+	return -1
+}
+
+// RemoveDuplicates returns a new slice with duplicate elements removed, preserving order
+func RemoveDuplicates[T comparable](slice []T) []T {
+	// TODO: Implement this function
+
+	m := map[T]bool{}
+	var res []T
+
+	for _, e := range slice {
+		if m[e] == true {
+			continue
+		}
+		res = append(res, e)
+		m[e] = true
+	}
+
+	return res
+}