Whiteboard to Xcode: Conquer Any iOS Coding Challenge

The 5-Step Framework for Acing Any Coding Challenge

Step 1: Listen, Clarify, and Understand

Step 2: Brainstorm and Whiteboard a High-Level Plan

Original: "hello"
Step 1: h ← → o
Step 2: e ← → l
Result: "olleh"

Step 3: Write Pseudocode

function reverseString(input):
    if input is empty or nil:
        return input
    
    convert string to character array
    set left pointer to 0
    set right pointer to last index
    
    while left < right:
        swap characters at left and right
        increment left
        decrement right
    
    return new string from array

Step 4: Translate to Clean Code in Xcode

func reverseString(_ input: String?) -> String? {
    // Handle edge cases
    guard let input = input, !input.isEmpty else {
        return input
    }
    
    // Convert to array for easier manipulation
    var characters = Array(input)
    var leftIndex = 0
    var rightIndex = characters.count - 1
    
    // Swap characters from both ends
    while leftIndex < rightIndex {
        characters.swapAt(leftIndex, rightIndex)
        leftIndex += 1
        rightIndex -= 1
    }
    
    return String(characters)
}

Step 5: Test, Analyze, and Refactor

Common Types of iOS Coding Challenges

Data Structures and Algorithms

// Find two numbers that sum to a target
func twoSum(_ nums: [Int], _ target: Int) -> [Int]? {
    var dict = [Int: Int]()
    
    for (index, num) in nums.enumerated() {
        let complement = target - num
        if let complementIndex = dict[complement] {
            return [complementIndex, index]
        }
        dict[num] = index
    }
    
    return nil
}

UI-Focused Challenges

class ProfileCardView: UIView {
    private let imageView = UIImageView()
    private let nameLabel = UILabel()
    private let bioLabel = UILabel()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        setupViews()
        setupConstraints()
    }
    
    private func setupViews() {
        backgroundColor = .systemBackground
        layer.cornerRadius = 12
        layer.shadowOpacity = 0.1
        
        imageView.contentMode = .scaleAspectFill
        imageView.clipsToBounds = true
        imageView.layer.cornerRadius = 40
        
        nameLabel.font = .boldSystemFont(ofSize: 18)
        bioLabel.font = .systemFont(ofSize: 14)
        bioLabel.numberOfLines = 0
        
        [imageView, nameLabel, bioLabel].forEach {
            $0.translatesAutoresizingMaskIntoConstraints = false
            addSubview($0)
        }
    }
    
    private func setupConstraints() {
        NSLayoutConstraint.activate([
            imageView.topAnchor.constraint(equalTo: topAnchor, constant: 16),
            imageView.centerXAnchor.constraint(equalTo: centerXAnchor),
            imageView.widthAnchor.constraint(equalToConstant: 80),
            imageView.heightAnchor.constraint(equalToConstant: 80),
            
            nameLabel.topAnchor.constraint(equalTo: imageView.bottomAnchor, constant: 12),
            nameLabel.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 16),
            nameLabel.trailingAnchor.constraint(equalTo: trailingAnchor, constant: -16),
            
            bioLabel.topAnchor.constraint(equalTo: nameLabel.bottomAnchor, constant: 8),
            bioLabel.leadingAnchor.constraint(equalTo: nameLabel.leadingAnchor),
            bioLabel.trailingAnchor.constraint(equalTo: nameLabel.trailingAnchor),
            bioLabel.bottomAnchor.constraint(equalTo: bottomAnchor, constant: -16)
        ])
    }
}

API Integration and Asynchronous Tasks

struct User: Codable {
    let id: Int
    let name: String
    let email: String
}

class UserService {
    enum APIError: Error {
        case invalidURL
        case noData
        case decodingError
    }
    
    func fetchUsers() async throws -> [User] {
        guard let url = URL(string: "https://api.example.com/users") else {
            throw APIError.invalidURL
        }
        
        let (data, _) = try await URLSession.shared.data(from: url)
        
        do {
            let users = try JSONDecoder().decode([User].self, from: data)
            return users
        } catch {
            throw APIError.decodingError
        }
    }
}

// In your view controller
class UsersViewController: UIViewController {
    @IBOutlet weak var tableView: UITableView!
    private var users: [User] = []
    private let userService = UserService()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        loadUsers()
    }
    
    private func loadUsers() {
        Task {
            do {
                users = try await userService.fetchUsers()
                await MainActor.run {
                    tableView.reloadData()
                }
            } catch {
                // Handle error - show alert or empty state
                print("Failed to load users: \(error)")
            }
        }
    }
}

Communicating Your Thought Process: The Meta-Skill

Thinking Out Loud

"So we need to find if two strings are anagrams. My first thought is to sort both strings and compare them - that would be O(n log n). But actually, since we're dealing with characters, I could use a frequency map instead. That would be O(n) time but use O(k) space where k is the number of unique characters. Given that we're probably dealing with ASCII or Unicode, the space is bounded, so I think the frequency map approach is better."

Receiving Feedback Gracefully

Conclusion

References