Valid Palindrome
A easy-tier problem at 51% community acceptance, tagged with Two Pointers, String. Reported in interviews at Cadence and 31 others.
Valid Palindrome is the two-pointer warm-up that shows up across 32+ companies, from Cadence and RBC to Spotify and Bank of America. On paper it looks trivial: check if a string reads the same forwards and backwards, ignore spaces and punctuation. In reality, candidates blank on case sensitivity, character filtering, and pointer logic under live assessment pressure. The 50% acceptance rate reflects how many people rush it and submit broken edge-case handling. If this problem hits your assessment and you freeze on the filtering logic, StealthCoder surfaces a clean two-pointer solution in seconds, invisible to the proctor.
Companies that ask "Valid Palindrome"
Valid Palindrome 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 a working Amazon engineer who got tired of watching qualified friends bomb OAs they'd solve cold in an IDE.
Get StealthCoderThe trap is thinking you can just reverse the string and compare. You can, but that wastes space and looks sloppy in interviews. The real pattern is two pointers closing inward: one at each end, both skipping non-alphanumeric characters, both comparing lowercase versions of valid characters. Most candidates mess up the character-checking logic (forgetting to handle numbers), the case conversion (forgetting toLowerCase or toLopper), or the pointer movement (advancing both pointers even when one skipped a character). Walk through 'A man, a plan, a canal: Panama' mentally and you'll see the pattern. StealthCoder handles the nitty filtering and pointer dance so if you hit this live and the two-pointer rhythm escapes you, you've got a working reference in seconds.
Pattern tags
You know the problem.
Make sure you actually pass it.
Valid Palindrome recycles across companies for a reason. It's easy-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 a working Amazon engineer who got tired of watching qualified friends bomb OAs they'd solve cold in an IDE. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Valid Palindrome interview FAQ
Is Valid Palindrome still asked at top companies?+
Yes. It appears across 32+ reported companies including Spotify, Bank of America, and Cadence. It's a favorite warm-up or screen-pass problem, so treat it as interview-ready territory. The 50% acceptance rate suggests it's still tripping up candidates in real assessments.
What's the trick to Valid Palindrome?+
Two pointers closing inward, skipping non-alphanumeric characters and comparing lowercase characters. The gotcha is the filtering logic: many people forget to handle digits or mess up case conversion. Filter once, pointer twice.
Does Valid Palindrome use String and Two Pointers topics together?+
Exactly. It's a textbook String problem solved cleanly with Two Pointers. Understanding both patterns matters: you're scanning a String structure with a pointer technique. It's a common pairing in assessments.
How does difficulty EASY rating match the 50% acceptance rate?+
EASY rating reflects the conceptual simplicity, not the implementation details. The 50% acceptance rate shows that filtering, case handling, and pointer movement trip people up under live interview conditions. Don't underestimate it.
What edge cases break Valid Palindrome solutions?+
Empty strings, single characters, strings with only spaces or punctuation, mixed case with numbers, and off-by-one pointer logic. Test 'a.' (one char plus punctuation) and '0P' (zero and letter) to catch filtering bugs early.
Want the actual problem statement? View "Valid Palindrome" on LeetCode →