iOS (Swift/SwiftUI) or Android (Kotlin/Compose). Adds app lifecycle, memory, offline-first, push notifications, store submission.
Primary categories: mobile · cs-fundamentals
Apple ICT3+ canonical system design. Tests asymmetric crypto, multi-device key fan-out, offline delivery, and the privacy-first architecture Apple grades senior candidates on.
Trade space for time using a hash map to convert O(n²) pair-finding into O(n) single-pass lookups. Foundation pattern behind dozens of LC problems.
BLE crowdsourced location, on-device crypto, anti-stalking, lost mode, battery-aware. Apple-specific signature SDI.
Cross-device sync, conflict resolution, on-device + cloud, privacy-preserving. Apple signature SDI.
End-to-end encryption (Signal protocol), message delivery guarantees, group chat, read receipts, multi-device. Meta signature SDI.
Photo upload + feed + stories + search/explore + hashtags. E5+ Meta product-design canon.
Structured story format used by every Mag7 behavioral round. Google extends to STAR-L (Learnings). Amazon expects 1 LP per story. Netflix tunes to culture pillars.