Graph and Tree Walks

Graphs are the other topic Twilio's onsite asks most, next to class design. The input is rarely a graph yet. It usually arrives as a flat list of rows, and turning that list into something you can search is half the work.

The three problems below start with a reachability question. Next is a hierarchy built from flat rows, asked as a two-part phone screen, and the last is a grouping problem that's a job for union-find.

Say which way each edge points before you build anything, since an edge one way says nothing about the way back. Then pick the search. A stack and a seen set cover most of it. Recursion is fine when the depth is small, and union-find fits when you only need to know who is grouped with whom.

TwilioPremium lesson · Coding round

The 3 Twilio problems are below.

1. 1A Premium questionCoding · Medium
2. 2A Premium questionCoding · Medium
3. 3A Premium questionCoding · Medium

Each with hints, the follow-up and a tested solution.

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From 197 Twilio reports, forum threads behind logins and write-ups in Chinese.

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