Rotate String
A easy-tier problem at 64% community acceptance, tagged with String, String Matching. Reported in interviews at Rivian and 6 others.
Rotate String is an easy string matching problem that shows up regularly at Rivian, Amdocs, SAP, Wells Fargo, Visa, TCS, and Zoho. The acceptance rate is 64%, which means a solid chunk of candidates still fumble it in live assessments. The trap is obvious: you think you need to manually rotate the string character by character, build new strings, and compare. That approach works but it's inefficient and error-prone under time pressure. The real trick lives in string concatenation and a single search operation. If this problem hits your live assessment and you blank on the pattern, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Rotate String"
Rotate String 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 for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe problem asks whether string s can become string goal by rotating s. A rotation means moving characters from the start to the end repeatedly. Most candidates start writing loop-based rotation logic, which is verbose and bug-prone. The elegant solution exploits a mathematical property: if s is a rotation of goal, then s will always appear as a substring within goal concatenated with itself (goal + goal). For example, if goal is 'abcd' and s is 'cdab', then 'cdab' appears in 'abcdabcd'. This reduces the problem to a single substring search, which handles edge cases like length mismatches automatically. The topics are String and String Matching, and this problem is a clean example of how string matching algorithms can solve problems that look like they need iteration. StealthCoder handles this pattern match instantly if you hit it during screen share.
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Rotate String 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 for the engineer who has done the work but might still blank with a webcam pointed at him. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Rotate String interview FAQ
Why is the manual rotation approach slow?+
Rotating character-by-character and comparing each result is O(n squared) or worse. You're rebuilding strings repeatedly and doing multiple full comparisons. The concatenation trick reduces it to O(n) because modern string search (like KMP) runs in linear time. Under live assessment pressure, the naive approach also introduces off-by-one bugs.
Is Rotate String still asked at these companies?+
Yes. Seven major companies report asking it, including Visa, Wells Fargo, and SAP. The 64% acceptance rate suggests it's not a rare edge case. It's a screening problem that filters for pattern recognition and knowledge of string matching tricks.
What's the trick to remembering the concatenation solution?+
Think about it visually. If you tape two copies of the string together, every possible rotation appears as a contiguous substring. It's a one-liner check: 'if s in goal + goal and len(s) == len(goal)'. The length check handles cases where s and goal are different sizes.
How does this relate to String Matching?+
String Matching is about finding patterns within text. This problem disguises a rotation detection as a substring search. Once you frame rotation as a matching problem (does s match a substring in goal + goal), the String Matching topic becomes the key insight.
What's the edge case that breaks naive solutions?+
If s and goal have different lengths, no rotation can make them equal. Many hand-coded rotation loops forget this check and loop infinitely or crash. The concatenation approach handles it automatically because the substring search will fail if lengths don't match.
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