Ticker Trie & String Matching

One of SIG's phone screens is a trie problem, and it wears a trading-desk costume. You are handed a list of company-to-ticker pairs and a stream of news headlines. Load the company names into a trie with the ticker sitting at each terminal node, then scan a headline and hand back every ticker it mentions. The interviewer will tell you plainly that being able to build a trie quickly is the test. Choose the structure and get the traversal right; there is no algorithm to invent.

The finance framing is not decoration. SIG trades on news, and a headline like "Big global company beats estimates" has to fan out to every instrument it could move. The same trie also powers the humbler feature next to it: a ticker box that completes what a trader starts typing. Both jobs are the same data structure asked two ways, so you build it once and traverse it two ways. This lesson drills both, starting with the autocomplete warm-up the screen tends to open on, then the headline scan it tests.