Google·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Google SWE coding round with a string matching problem that looks deceptively simple until you realize the edge cases stack up fast. Classic Google style where the problem statement is clean but the implementation isn't.

Questions Asked (1)

Given a dictionary of words and a 'jammed' string where keys on a keyboard can repeat characters (but never drop, insert, or reorder them), return all words from the dictionary that could have produced the jammed string.

Algorithms & Data Structures

Author's notes

The core idea clicked pretty quickly: each character in the original word just needs to match a consecutive run of the same character in the jammed string, in order.

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AI HintsAI Generated

Suggested Approach

Clarify that the jammed string is formed by repeating characters in each word without dropping, inserting, or reordering. Then, for each dictionary word, check if it can be transformed into the jammed string by expanding each character into a run of the same character. Use a two-pointer technique to efficiently compare the word and the jammed string.

Pro tip: After presenting the solution, mention that you can optimize by grouping dictionary words by their run-length encoding pattern, allowing you to quickly filter candidates. This shows you think about scalability and practical optimizations.

1. Clarify the problem

Confirm that the jammed string is formed by repeating characters in each word, with no insertions, deletions, or reordering. Ensure you understand that each character in the original word can appear one or more times consecutively in the jammed string.

2. Define the matching condition

Two strings match if they have the same sequence of distinct characters and the count of each character in the jammed string is at least the count in the original word. This means the jammed string's run lengths must be >= the word's run lengths for corresponding characters.

3. Design an efficient algorithm

Use a two-pointer approach to compare each dictionary word with the jammed string. Iterate through both strings simultaneously, advancing pointers and checking that characters match and run lengths are compatible. This runs in O(n) per word, where n is the length of the jammed string.

4. Handle edge cases

Consider cases where the word is longer than the jammed string, characters don't match, or run lengths are insufficient. Also, handle empty strings and ensure the algorithm correctly returns an empty list if no words match.

5. Optimize and discuss trade-offs

Mention that you can preprocess the dictionary by grouping words with the same run-length encoding pattern, reducing the number of comparisons. Discuss time and space complexity: O(D * L) naive, where D is dictionary size and L is jammed string length, and how grouping can improve average performance.

Key Points to Mention

Two-pointer technique for comparing strings with run-length constraints
Run-length encoding (RLE) to represent strings as sequences of (character, count) pairs
Time complexity analysis: O(D * L) where D is dictionary size and L is jammed string length
Edge cases: empty strings, mismatched characters, insufficient repetitions
Optimization by grouping dictionary words by their RLE pattern
Clarifying assumptions about the jammed string formation

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