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read.ai·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
Jun 2026

Summary

Got a coding question from read.ai that was basically a graph/union-find problem dressed up as a sentence similarity check. Pretty classic algorithmic interview, nothing too surprising about the format.

Questions Asked (1)

Q1

Given two sentence arrays and a list of similar word pairs where similarity is transitive, determine if the two sentences are similar (same length, each corresponding word pair is identical or in the same similarity group).

Algorithms & Data Structures
Author's notes

The transitivity part is what makes this tricky.

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AI HintsAI Generated

Suggested Approach

Model the similarity relationships as a graph and use union-find (disjoint set union) to group words that are transitively similar. Then iterate through both sentences, checking that lengths match and each word pair is either identical or belongs to the same similarity group.

Pro tip: Mention that you can optimize by only building groups for words that appear in the sentences, and use path compression and union by rank for near-constant time operations. This shows you consider practical performance beyond the basic algorithm.

1. Clarify requirements and edge cases

Confirm that similarity is transitive, that sentences must be of equal length, and that identical words are always similar. Ask about case sensitivity and whether similarity pairs are bidirectional.

2. Choose the right data structure

Select union-find (disjoint set union) to efficiently group words based on the given similar pairs, leveraging transitivity. Alternatively, build an adjacency list and run BFS/DFS, but union-find is simpler and faster for this use case.

3. Build similarity groups

Initialize each unique word as its own set, then union each pair from the similar word pairs list. After processing all pairs, words in the same set are considered similar.

4. Compare sentences word by word

First check if the sentences have the same length; if not, return false. Then iterate through corresponding words: if they are identical, continue; otherwise, check if they belong to the same similarity group using find operations.

5. Analyze complexity and test

State the time complexity: O(N + P α(N)) where N is total words and P is number of pairs, with near-constant α due to path compression. Walk through examples, including edge cases like empty sentences or words not in any pair.

Key Points to Mention

  • Union-Find (Disjoint Set Union) with path compression and union by rank for efficient grouping.
  • Transitivity of similarity means if A~B and B~C, then A~C, which union-find naturally handles.
  • Length check first: if sentences have different lengths, they cannot be similar.
  • Identical words are always similar, so no need to check groups for them.
  • Time complexity: O(N + P α(N)) where N is total words and P is number of similar pairs.
  • Space complexity: O(U) where U is number of unique words in the sentences and pairs.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.