Regular Expression Matching
A hard-tier problem at 29% community acceptance, tagged with String, Dynamic Programming, Recursion. Reported in interviews at Hiver and 22 others.
Regular Expression Matching is a hard problem that sits at the intersection of string parsing and dynamic programming. Companies like Airbnb, ByteDance, Snowflake, and Confluent ask it frequently. The challenge: implement a regex matcher that supports '.' (any character) and '*' (zero or more of the preceding element). With a 29% acceptance rate, most candidates either freeze on the state-space design or code a solution that works on examples but fails on edge cases around '*' and empty matches. If this problem hits your live assessment and you blank on the DP transition, StealthCoder solves it in seconds, invisible to the proctor.
Companies that ask "Regular Expression Matching"
Regular Expression Matching is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an Amazon engineer who realized the OA tests how well you memorized 200 problems, not how well you code.
Get StealthCoderThe trap is thinking greedily or recursively without memoization. The actual solution requires dynamic programming with a 2D table where dp[i][j] represents whether the first i characters of the string match the first j characters of the pattern. The trick: '*' can match zero characters (skip it entirely) or one-or-more characters (if the preceding element matches). Most candidates miss the zero-match case or don't handle the order of transitions correctly. Recursion works but times out without memoization. The pattern itself has no length constraint in typical versions, so your DP table grows quadratically. When you hit this live and the obvious string-comparison approach crumbles under edge cases like 'a*b*c*', StealthCoder delivers the full DP state machine.
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Regular Expression Matching recycles across companies for a reason. It's hard-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an Amazon engineer who realized the OA tests how well you memorized 200 problems, not how well you code. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Regular Expression Matching interview FAQ
Is this really still asked at FAANG?+
Yes. The input data shows it's been reported by at least 10 top-tier companies including Airbnb, ByteDance, and Snowflake. It's a classic screener problem because it tests both algorithmic thinking and implementation discipline under pressure.
What's the trick everyone misses?+
The '*' operator can match zero instances of the preceding character. Candidates often code the one-or-more case but forget to skip the '*' entirely. The DP transition must handle both: skip the pattern character (if it's '*'), or advance both pointers if the current characters match.
Will recursion with memoization pass?+
Yes, but it's error-prone. Bottom-up DP is safer because you build the table in order and avoid stack-overflow risk. Both work if memoization or table-building is done correctly. Most fails come from incorrect transition logic, not the approach itself.
How does this relate to the other string and DP topics?+
It combines String pattern matching with Dynamic Programming state design. It's harder than basic DP because the state (string index, pattern index) interacts with a tricky pattern rule ('*'). Recursion shows the logic clearly, but DP avoids repeated subproblems.
What are the common edge cases?+
Empty string with pattern 'a*b*c*' (matches), pattern like '*a' (invalid, but some versions allow it), single '*' with non-empty string, and strings with repeated characters. Test with 'aa' and pattern 'a*a*' to verify your zero-match logic.
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