Valid Palindrome III
A hard-tier problem at 49% community acceptance, tagged with String, Dynamic Programming. Reported in interviews at Meta and 0 others.
Valid Palindrome III is a hard string problem that Meta has asked. With a ~49% acceptance rate, this one separates candidates who can spot the DP pattern from those who get lost in brute force. The trick isn't obvious from the problem statement: you're not just checking if a string is a palindrome, you're deciding which minimum number of characters to delete to make it one. If you haven't drilled edit-distance or subsequence DP recently, this is the exact spot where you blank on the live OA. StealthCoder solves it in seconds when you hit that moment.
Companies that ask "Valid Palindrome III"
Valid Palindrome III 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. Made by an Amazon engineer who watched the leaked-problem repo become an industry secret. He decided you should have it too.
Get StealthCoderThe gotcha here is that a greedy or simple two-pointer approach fails. You need dynamic programming to track the minimum deletions required across all substrings. The core insight is that a string is a valid palindrome after deletions if and only if the longest palindromic subsequence equals the string length minus the number of deletions. Most candidates start with a recursive attempt, hit exponential time, then either bail or build a memoization table without clarity on state transitions. Common pitfall: confusing this with longest palindromic subsequence directly. The DP table needs clean recurrence: either the characters at both ends match (move inward) or they don't (try both deletion options and take the minimum). StealthCoder is your safety net if you freeze during the live assessment on this pattern.
Pattern tags
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Make sure you actually pass it.
Valid Palindrome III 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. Made by an Amazon engineer who watched the leaked-problem repo become an industry secret. He decided you should have it too. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Valid Palindrome III interview FAQ
Is Valid Palindrome III still asked at Meta in 2024?+
Yes. Meta is the only company in reported data asking this problem. It's a targeted hard problem for senior or specialized rounds. If you're interviewing with Meta, especially for a role that emphasizes algorithms, treat this as a likely encounter.
What's the actual trick I need to know?+
The trick is recognizing this as a DP state-compression problem, not a greedy one. You build a 2D table where dp[i][j] = minimum deletions to make substring from i to j a palindrome. If characters match, dp[i][j] = dp[i+1][j-1]. Otherwise, dp[i][j] = 1 + min(dp[i+1][j], dp[i][j-1]). No clever observation bypasses this.
How does this relate to String and Dynamic Programming topics?+
Both deeply. The String aspect is parsing and understanding palindrome constraints. The DP aspect is modeling the search space (all substrings) and choosing the optimal subproblem decomposition. You can't solve this with string manipulation alone; you need memoized recursion or tabulation.
Why is the acceptance rate so low at ~49%?+
Hard difficulty, unfamiliar DP recurrence, and time pressure. Most candidates see 'palindrome' and try two-pointer logic or brute-force subsequence checks. Realizing it's a min-cost edit problem requires pattern recognition that takes time to develop.
What should I practice before the OA?+
Work through longest palindromic subsequence first, then edit distance (Levenshtein). Both use similar DP table shapes. Then tackle this problem by writing out the recurrence on paper before coding. Coding without a clear recurrence is where most candidates lose 10+ minutes.
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