63 lines
2.2 KiB
Swift
63 lines
2.2 KiB
Swift
/// A basic stack type implementing the LIFO principle - only the last inserted element can be accessed and removed.
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public struct Stack<Element> {
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private var elements = [Element]()
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/// Creates an empty `Stack`.
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public init() {}
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/// The number of elements in this stack.
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public var count: Int {
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elements.count
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}
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/// Pushes (appends) an element onto the stack.
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///
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/// - parameter element: The element to push onto the stack.
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public mutating func push(_ element: Element) {
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elements.append(element)
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}
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/// Removes and returns the last element of the stack.
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///
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/// - returns: The last element of the stack if the stack is not empty; otherwise, nil.
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@discardableResult
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public mutating func pop() -> Element? {
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elements.popLast()
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}
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/// Returns the last element of the stack if the stack is not empty; otherwise, nil.
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public func peek() -> Element? {
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elements.last
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}
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/// Check whether the sequence contains an element that satisfies the given predicate.
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///
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/// - parameter predicate: A closure that takes an element of the sequence
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/// and returns whether it represents a match.
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/// - returns: `true` if the sequence contains an element that satisfies `predicate`.
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public func contains(where predicate: (Element) -> Bool) -> Bool {
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elements.contains(where: predicate)
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}
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/// Modify the last element.
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///
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/// - parameter modifier: A function to applied to the last element to modify it in place.
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public mutating func modifyLast(by modifier: (inout Element) -> Void) {
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if elements.isNotEmpty {
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modifier(&elements[count - 1])
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}
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}
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}
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extension Stack: CustomDebugStringConvertible where Element == CustomDebugStringConvertible {
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public var debugDescription: String {
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let intermediateElements = count > 1 ? elements[1 ..< count - 1] : []
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return """
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Stack with \(count) elements:
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first: \(elements.first?.debugDescription ?? "")
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intermediate: \(intermediateElements.map(\.debugDescription).joined(separator: ", "))
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last: \(peek()?.debugDescription ?? "")
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"""
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}
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}
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