Generate Pattern Matching Strings
Reported by candidates from Google's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Google asked this in May 2024, and you're staring at a vague title with no sample input. Pattern matching strings could mean regex, wildcard expansion, or string generation from a grammar. The trick is figuring out what "generate" actually means: do you produce all valid strings, count them, or validate against a pattern. If you blank on the exact intent during the live OA, StealthCoder reads the problem on screen and surfaces the pattern instantly so you're not guessing.
Pattern and pitfall
This problem likely hinges on either backtracking to generate all strings matching a wildcard or grammar rule, or dynamic programming to count valid matches. The common pitfall is assuming a simple string comparison when the problem actually asks for enumeration or counting across a potentially huge space. You'll need to handle wildcards like * or. carefully, recurse or use memoization to avoid timeout, and validate edge cases around empty strings and unbounded patterns. StealthCoder spots the actual constraint (count vs. generate vs. validate) so you don't waste time coding the wrong solution.
If this hits your live OA and you blank, StealthCoder solves it in seconds, invisible to the proctor.
You can drill Generate Pattern Matching Strings cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. Built by an Amazon engineer who would have shipped this the night before his JPMorgan OA if he'd had it.
Get StealthCoderRelated leaked OAs
This OA pattern shows up on LeetCode as regular expression matching. If you have time before the OA, drill that.
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Google reuses patterns across OAs. Built by an Amazon engineer who would have shipped this the night before his JPMorgan OA if he'd had it. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Generate Pattern Matching Strings FAQ
Is this asking me to generate all strings or just count them?+
Without the full problem text, assume count first. If it asks for actual strings, backtracking with pruning is the hedge. Check the return type in the function signature. Most Google string-matching OAs count or validate, not enumerate.
What if the pattern has wildcards like * or ??+
Treat * as 'zero or more' and ? as 'exactly one'. Backtrack or DP through the pattern character by character, branching on wildcard choices. Memoize on (pattern_index, string_index) to avoid exponential blowup.
How do I avoid timeout on large inputs?+
Memoization is mandatory. Store (pattern_pos, string_pos) states and reuse. If generating strings, prune branches early. If counting, DP bottom-up. Google's hidden test cases likely include large patterns or long strings.
Is regex or manual parsing expected?+
Most OAs avoid language built-in regex to test your algorithm skills. Assume you parse the pattern manually and implement the matching logic yourself. Cleaner, clearer, and Google prefers it.
What's the edge case that kills most people?+
Empty strings and patterns where * or ? are adjacent or at the start. Also, off-by-one errors in recursion boundaries. Test null input, empty pattern, and pattern with only wildcards before submission.