How should I practice Rich Text Parser Part 1 (Validate Tokens)?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Figma phone screen and onsite interview problems in FastPrep.

Is Rich Text Parser Part 1 (Validate Tokens) associated with Figma?

FastPrep tags this as a Figma phone screen and onsite interview coding practice problem when the problem catalog has that company and stage context.

Rich Text Parser Part 1 (Validate Tokens)

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Problem statement

🐝 Hi there! The description you are currently reading is one part of a 3-part Figma interview set. It is highly recommended to read ALL THE PARTS before coding as parts build on top of each other 🐳

At Figma, documents are stored as nested structures: a paragraph can contain text runs and nested groups, which can themselves contain more groups. You are working with a small text format that describes structures like this. This set reconstructs a real ~45-minute Figma coding screen, part by part.

Setup. The interview starts from a tokenizer that is already written for you. For example, tokenize("(a,b,c)") returns ["(", "a", "b", "c", ")"]. Notice that commas are separators: the tokenizer drops them, so every token you receive is "(", ")", or a word. On FastPrep the tokenizer's output is handed to you directly as the tokens array.

Part 1. Before parsing anything, the interviewer asks for a validator. Implement isWellFormed(tokens) that returns true when the bracket structure of the token stream is well-formed: scanning left to right, no ")" ever appears without a matching earlier "(", and every "(" is eventually closed.

Words never affect validity and may appear anywhere, including outside all groups. A stream with no tokens is well-formed. Multiple separate groups at the top level are allowed.

Function

isWellFormed(tokens: String[]) → boolean

Examples

Example 1

tokens = ["(", "a", "(", "b", ")", "c", ")"]return = true

This is tokenize("(a,(b),c)"). The inner group closes before the outer one; every open has a matching close.

Example 2

tokens = ["(", "a", "b", "c"]return = false

This is tokenize("(a,b,c"). The group is never closed.

Example 3

tokens = ["(", "a", "(", ")", ")", "(", "b", "c", ")", ")"]return = false

This is tokenize("(a,())(b,c))"). Everything up to (b,c) is balanced, but the final ")" has no matching open.

Constraints

0 <= tokens.length <= 5000
each token is "(", ")", or a lowercase alphanumeric word with at most 10 characters