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Merge pull request #2 from prolificinteractive/feature/linked-list-da…
…ta-structure Added linked list data structure
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187 changes: 187 additions & 0 deletions
187
DevKit/DevKit/Classes/Data Structures/Linked List/LinkedList.swift
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,187 @@ | ||
| // | ||
| // LinkedList.swift | ||
| // DevKit | ||
| // | ||
| // Created by Thibault Klein on 8/30/18. | ||
| // Copyright © 2018 Jonathan Samudio. All rights reserved. | ||
| // | ||
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| import Foundation | ||
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| /// Linked List. | ||
| /// A linked list is a linear collection of data elements where each element points to the next. A linked list has several theoretical advantages over contiguous storage options such as the Swift Array: | ||
| /// - Constant time insertion and removal from the front of the list. | ||
| /// - Reliable performance characteristics. | ||
| /// | ||
| /// | ||
| /// - Note: | ||
| /// Use a linked list over a Swift array if you need to store a large amount of data and you need to perform | ||
| /// insertions and removals from any position in the sequence. | ||
| /// | ||
| /// Do not use a linked list if you need indexing, sorting, random access to the data or sequence traversal from the back of the sequence to the front. | ||
| /// | ||
| /// - Warning: Due to the fact that each node has a reference to the next node, the memory footprint of a linked list can have a negative impact on the device if the list becomes extremely large. | ||
| open class LinkedList<T> { | ||
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| // MARK: - Public Properties | ||
| public var head: LinkedListNode<T>? | ||
| public var tail: LinkedListNode<T>? | ||
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| /// `true` if the linked list is empty. `false` if not. | ||
| public var isEmpty: Bool { | ||
| return head == nil | ||
| } | ||
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| // MARK: - Initialization | ||
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| public init() { } | ||
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| // MARK: - General Functions | ||
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| // MARK: - Public Functions | ||
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| /// Returns the linked list head's value. | ||
| /// | ||
| /// - Returns: The head's value. | ||
| public func peek() -> T? { | ||
| return head?.value | ||
| } | ||
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| /// Returns the node at the given index, or nil if the node can't be found. | ||
| /// | ||
| /// - Complexity: O(n) | ||
| /// - Parameter index: The index to use. | ||
| /// - Returns: The node at the given index. | ||
| public func node(at index: Int) -> LinkedListNode<T>? { | ||
| var currentIndex = 0 | ||
| var currentNode = head | ||
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| while let current = currentNode, currentIndex != index { | ||
| currentNode = current.next | ||
| currentIndex += 1 | ||
| } | ||
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| return currentNode | ||
| } | ||
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| // MARK: Adding Functions | ||
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| /// Adds a value at the beginning of the linked list. | ||
| /// | ||
| /// - Complexity: O(1) | ||
| /// - Parameter value: The value to add. | ||
| /// - Returns: The newly added node. | ||
| @discardableResult | ||
| public func push(_ value: T) -> LinkedListNode<T> { | ||
| guard !isEmpty else { | ||
| head = LinkedListNode(value: value) | ||
| tail = head | ||
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| return head! | ||
| } | ||
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| let node = LinkedListNode(value: value, next: head) | ||
| head = node | ||
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| return node | ||
| } | ||
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| /// Appends a value at the end of the linked list. | ||
| /// | ||
| /// - Complexity: O(1) | ||
| /// - Parameter value: The value to add. | ||
| /// - Returns: The newly added node. | ||
| @discardableResult | ||
| public func append(_ value: T) -> LinkedListNode<T> { | ||
| guard !isEmpty else { | ||
| return push(value) | ||
| } | ||
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| let node = LinkedListNode(value: value) | ||
| tail?.next = node | ||
| tail = node | ||
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| return node | ||
| } | ||
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| /// Inserts a value after the given node. | ||
| /// | ||
| /// - Complexity: O(1) | ||
| /// - Parameters: | ||
| /// - value: The value to insert. | ||
| /// - node: The node to add after. | ||
| /// - Returns: The newly added node. | ||
| @discardableResult | ||
| public func insert(value: T, after node: LinkedListNode<T>) -> LinkedListNode<T> { | ||
| guard tail !== node else { | ||
| return append(value) | ||
| } | ||
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| let newNode = LinkedListNode(value: value) | ||
| newNode.next = node.next | ||
| node.next = newNode | ||
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| return newNode | ||
| } | ||
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| // MARK: Removing Functions | ||
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| /// Removes the value at the top of the list. | ||
| /// | ||
| /// - Complexity: O(1) | ||
| /// - Returns: The value at top of the list. | ||
| public func pop() -> T? { | ||
| defer { | ||
| head = head?.next | ||
| if isEmpty { | ||
| tail = nil | ||
| } | ||
| } | ||
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| return head?.value | ||
| } | ||
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| /// Removes the last node of the list. | ||
| /// | ||
| /// - Complexity: O(n) | ||
| /// - Returns: The value at the end of the list. | ||
| public func removeLast() -> T? { | ||
| guard !isEmpty else { | ||
| return nil | ||
| } | ||
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| guard head?.next != nil else { | ||
| return pop() | ||
| } | ||
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| var prev = head | ||
| var currentNode = head?.next | ||
| while currentNode?.next != nil { | ||
| currentNode = currentNode?.next | ||
| prev = prev?.next | ||
| } | ||
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| prev?.next = nil | ||
| tail = prev | ||
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| return currentNode?.value | ||
| } | ||
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| /// Removes the node after the given node. | ||
| /// | ||
| /// - Complexity: O(1) | ||
| /// - Parameter node: The node to use. | ||
| /// - Returns: The value removed. | ||
| @discardableResult | ||
| public func remove(after node: LinkedListNode<T>) -> T? { | ||
| defer { | ||
| if node.next === tail { | ||
| tail = node | ||
| } | ||
| node.next = node.next?.next | ||
| } | ||
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| return node.next?.value | ||
| } | ||
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| } |
25 changes: 25 additions & 0 deletions
25
DevKit/DevKit/Classes/Data Structures/Linked List/LinkedListNode.swift
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,25 @@ | ||
| // | ||
| // LinkedListNode.swift | ||
| // DevKit | ||
| // | ||
| // Created by Thibault Klein on 8/30/18. | ||
| // Copyright © 2018 Jonathan Samudio. All rights reserved. | ||
| // | ||
|
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| import Foundation | ||
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| /// Describes a node in a linked list. | ||
| open class LinkedListNode<T> { | ||
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| // MARK: - Public Properties | ||
| public var value: T | ||
| public var next: LinkedListNode? | ||
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| // MARK: - Initialization | ||
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| public init(value: T, next: LinkedListNode? = nil) { | ||
| self.value = value | ||
| self.next = next | ||
| } | ||
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| } |
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