Reverse Prefix of Word
A easy-tier problem at 86% community acceptance, tagged with Two Pointers, String, Stack. Reported in interviews at Optum and 0 others.
Reverse Prefix of Word is an easy problem with an 86% acceptance rate, and it's been asked at Optum. The pattern is straightforward but the implementation details trip people up in live assessments. You're given a word and a character, and you need to reverse everything up to and including the first occurrence of that character, then return the result. If the character doesn't exist, return the word unchanged. It sounds simple until you realize the string operations and boundary checks under time pressure. StealthCoder runs invisibly during your OA and surfaces a clean solution the moment you hit a wall.
Companies that ask "Reverse Prefix of Word"
Reverse Prefix of Word 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 core pattern uses two pointers or a stack to reverse a prefix. Find the index of the target character first. If it doesn't exist, return the original word. If it does, reverse the substring from index 0 to that index (inclusive), then concatenate it with the rest of the word. Common mistakes include off-by-one errors on the substring slice, forgetting to handle the missing character case, or overthinking with unnecessary data structures. The two-pointer approach is cleanest: swap characters from both ends moving inward. A stack-based approach works too but adds overhead. The real gotcha is edge cases (single character, character at the end, character not found). Most candidates get 80% of test cases and fail on these. If you blank on the substring slicing or pointer logic during the actual assessment, StealthCoder executes the solution in seconds while you stay invisible to the proctor.
Pattern tags
You know the problem.
Make sure you actually pass it.
Reverse Prefix of Word 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.
Reverse Prefix of Word interview FAQ
Is this problem actually easy or does it trip up mid-level engineers?+
It's genuinely easy, with an 86% acceptance rate. Most people solve it. The trap is the live-assessment time crunch and off-by-one errors on slicing. You know the algorithm but rush the implementation. Optum has asked it, likely as a warmup or early-screen question.
What's the difference between solving this with two pointers vs a stack?+
Two pointers is faster and uses constant space. You find the split index, then reverse in-place on the substring. Stack approach builds the reversed prefix element-by-element, which wastes memory. Both hit the right answer, but two-pointers is what interviewers expect.
How does this relate to the String and Two Pointers topics?+
It's a direct application of both. The String topic covers substring extraction and concatenation. Two Pointers handles the reversal by swapping characters from opposite ends. If you're weak on either, you'll stumble. Stack is a bonus pattern for alternative solutions, not required.
What's the most common mistake on this problem?+
Off-by-one errors when finding the character index or slicing the prefix. Also forgetting to handle the case where the character doesn't exist in the word. These aren't logic gaps, they're typos under pressure. In a live OA, one typo fails multiple test cases.
Will knowing this pattern help me at other companies?+
It's a low-frequency ask outside Optum based on available data, but the techniques (two pointers, string slicing, boundary checks) appear constantly in harder problems. Master it because the pattern is foundational, not because it's asked everywhere.
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