SIG Software Engineer Onsite Coding Questions

LeetCode #2817: Minimum Absolute Difference Between Elements With Constraint. Difficulty: Medium. Topics: Array, Binary Search, Ordered Set. Asked at SIG in the last 6 months.

LeetCode #1743: Restore the Array From Adjacent Pairs. Difficulty: Medium. Topics: Array, Hash Table, Depth-First Search. Asked at SIG in the last 6 months.

LeetCode #48: Rotate Image. Difficulty: Medium. Topics: Array, Math, Matrix. Asked at SIG in the last 6 months.

## Problem Given a block of unstructured text (e.g., a financial news article), extract all valid US stock ticker symbols. A ticker is 1-5 uppercase letters. However, not every sequence of uppercase letters is a ticker — you must filter using a provided set of known valid tickers. ```python def find_tickers( text: str, valid_tickers: set[str] ) -> list[str]: """Return list of tickers found, in order of first appearance, deduplicated.""" ... ``` ``` text = "Investors are watching AAPL and GOOGL closely. The FDA approved MRNA." valid_tickers = {"AAPL", "GOOGL", "MRNA", "TSLA"} Output: ["AAPL", "GOOGL", "MRNA"] ``` ## Follow-ups 1. How do you distinguish the ticker `I` (Intelsat) from the word "I" in normal English text? What heuristics help? 2. Tickers can appear with punctuation around them (e.g., "(AAPL)", "AAPL,"). How does your regex handle this? 3. The valid_tickers set has 10,000 entries. Does set lookup remain O(1) in Python? How does this affect overall complexity? 4. A new ticker was listed today and is not yet in `valid_tickers`. How would you keep your ticker list fresh without manual updates?