Synonymous Sentences

Synonymous Sentences

What is this problem about?

In the Synonymous Sentences coding problem, you are given a list of pairs of synonyms and a sentence. You need to find all possible sentences that can be formed by replacing words with their synonyms. The synonym relationship is transitive, meaning if "big" is a synonym of "large" and "large" is a synonym of "huge", then "big" is also a synonym of "huge". Your output should be a list of sentences sorted in lexicographical order.

Why is this asked in interviews?

This question is asked by companies like Rippling and Cruise to test a candidate's ability to combine graph theory with backtracking. It requires you to first group all synonymous words into "equivalence classes" and then use those groups to generate all permutations of the sentence. It evaluates your skills in using Union Find (for grouping) and Recursion/Backtracking (for generation).

Algorithmic pattern used

The problem uses a combination of Union Find and Backtracking.

1. Union Find: Process the synonym pairs to group words into connected components. For example, {big, large, huge} would be one component.
2. Hash Table: Map each word to its component. Then, create a mapping from each component ID to a sorted list of all words in that component.
3. Backtracking: Split the sentence into words. For each word, if it belongs to a synonym group, iterate through every word in that group and recursively build the sentence. If it doesn't, just move to the next word.

Example explanation

Synonyms: [("happy", "joyful"), ("joyful", "glad")], Sentence: I am happy.

1. Union Find: {"happy", "joyful", "glad"} are synonyms.
2. Sorted group: ["glad", "happy", "joyful"].
3. Backtracking:
   • "I am glad"
   • "I am happy"
   • "I am joyful" All these sentences are generated and added to the results.

Common mistakes candidates make

A frequent mistake is forgetting the transitivity of synonyms, which is why Union Find is necessary. Another error is not sorting the synonyms within each group, which makes it harder to produce the final list of sentences in lexicographical order. Some candidates also struggle with the memory constraints when a sentence has many words that all have large synonym groups.

Interview preparation tip

When prepping for the Synonymous Sentences interview question, focus on the Union Find interview pattern to handle group memberships. Also, practice the Backtracking interview pattern for generating combinations or permutations. Understanding how to handle transitive relationships in a graph is a key skill for many complex string and data processing tasks.