iOS Scrollable Grid & Swift Concurrency

Build an iOS scrollable square grid, then answer Swift and GCD questions about value types, copy-on-write, memory, weak references, and dispatch ordering. Requirements For the iOS coding round, build a local app component in SwiftUI or UIKit: Render a scrollable square grid with fixed rows and columns. Change a cell's color when tapped. Make row and column counts externally configurable. Change each tapped cell to a random color. Navigate to a detail page showing the selected color. Allow color edits on the detail page to propagate back to the grid. Domain-specific Swift questions may include: Predicting output order for DispatchQueue.async and sync snippets. class vs struct and value semantics. Copy-on-write implementation. Stack vs heap. weak vs unowned and why unowned can crash. Implementing a dictionary without using the system dictionary as the backing store. Notes For SwiftUI, a clean implementation uses LazyVGrid, stable cell IDs, @State or observable state for cell colors, and a binding or callback to propagate detail edits. For UIKit, use UICollectionView with a diffable or simple data source. For GCD questions, reason about the current queue, whether sync blocks the caller, and whether queued async work has executed yet. For value-type questions, emphasize copy-on-write storage sharing until mutation. Preparation Build the grid in both SwiftUI and UIKit if you have time; at least know one path cold. Practice two GCD output-order snippets and narrate the queue state line by line. Implement a tiny hash table with buckets, collision handling, resize, get, put, and remove. Prepare concise explanations for ARC, weak, unowned, and retain cycles.