Swift Xcode more implementation of InterviewCake _Delete Linked List Node_ in generally O(1) time and O(1), with references side-effects. ⚠️ Spoiler alert: this is an improved answer to the https://www.interviewcake.com/question/swift/delete-node question, so no peeking!

InterviewCake-LinkedListNode+Extensions.swift

//
//  LinkedListNode+Extensions.swift
//
//  Copyright © 2018 Xavier Schott
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.
//

import Foundation

// Logging
extension LinkedListNode : CustomStringConvertible {
    var description: String {
        return (value as? CustomStringConvertible)?.description ?? ""
    }

    func log() {
        print(self)
    }
}

// Comparing nodes
extension LinkedListNode : Equatable {
    static func == (lhs: LinkedListNode, rhs: LinkedListNode) -> Bool {
        return lhs.value == rhs.value
    }
}

InterviewCake-LinkedListNode.swift

// LinkedListNode as presented in the exercise, untouched

import Foundation

class LinkedListNode<Value:Equatable> {
    var value: Value
    var next: LinkedListNode?

    init(_ value: Value) {
        self.value = value
    }
}

InterviewCake-NodeManipulator.swift

//
//  NodeManipulator.swift
//
//  Copyright © 2018 Xavier Schott
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.
//

import Foundation

class NodeManipulator<Element:Equatable> where Element:CustomStringConvertible {
    enum NodeManipulatorError: Error {
        case NodeNotFound
    }

    var root:LinkedListNode<Element>?

    init (_ list: LinkedListNode<Element>) {
        root = list
    }

    // No side effect, O(n)
    func deleteNodeSafely(node: LinkedListNode<Element>) throws {
        var i:LinkedListNode<Element>? = root
        var parent:LinkedListNode<Element>?

        while i != nil {
            if node == i {                  // Found it
                parent?.next = node.next    // Remove it
                if node == root {           // Reconnect root
                    root = node.next
                }
                return
            }
            parent = i
            i = i?.next
        }
        throw NodeManipulatorError.NodeNotFound
    }

    // Side effects on direct references, O(1) except for last node
    func deleteNode(node: LinkedListNode<Element>) throws {
        if let skip = node.next {
            node.value = skip.value
            node.next = skip.next
        } else {
            try deleteNodeSafely(node: node)
        }
    }

    func log() {
        var node:LinkedListNode<Element>? = root
        while node != nil {
            node?.log()
            node = node?.next
        }
    }
}

InterviewCake-NodeManipulatorTests.swift

//
//  NodeManipulatorTests.swift
//
//  Copyright © 2018 Xavier Schott
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.
//

import XCTest

class NodeManipulatorTests: XCTestCase {
    func testDeleteNode() {

        let a = LinkedListNode("A")
        let b = LinkedListNode("B")
        let c = LinkedListNode("C")

        a.next = b
        b.next = c
        
        let manipulator = NodeManipulator(a)

        do {
            try manipulator.deleteNode(node: b)
            manipulator.log() // Will print "A", "C"
        } catch {
            XCTAssert(false)
        }

        XCTAssert(true) // Not an actual test
    }
}