Modify Array
Reported by candidates from Paypal's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
You've got a PayPal OA coming in the next day or two, and Modify Array just landed in your inbox. This is a straightforward array manipulation problem, but the trick is in how you track state and avoid unnecessary rewrites. The pattern is direct: iterate, apply a rule, maybe track indices or values. StealthCoder sits invisible during your assessment, ready to feed you the solution if you freeze on the implementation details. Most candidates overthink the modification logic. Don't.
Pattern and pitfall
Modify Array typically asks you to change elements based on a condition, like doubling evens, removing duplicates, or applying a formula to a range. The gotcha is managing in-place edits versus building a new array, and whether order matters. You'll likely iterate once or twice, tracking what changes and what stays. Some versions use a two-pointer pattern if you're deleting or rearranging. The real speed comes from spotting early whether you can mutate in-place or need a fresh list. StealthCoder watches your screen, reads the exact prompt, and gives you the pattern in seconds so you don't waste 10 minutes on the wrong approach.
Drill it cold or hedge it with StealthCoder. Either way, don't walk into the OA hoping you remember the trick.
You can drill Modify Array cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. Made for the candidate who got the OA invite this morning and has 72 hours, not six months.
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Modify Array FAQ
Is this in-place or do I build a new array?+
The prompt will tell you. If it says 'modify array' without mentioning space, assume new array is fine. If it says 'in-place', watch the memory limit and use two pointers or index-shifting. Read the exact constraint first.
How hard is Modify Array really?+
It's a medium-easy problem. The logic is simple, but implementation details trip people up. Off-by-one errors, forgetting to handle edge cases like empty arrays, or writing inefficient loops. Spend 2 minutes reading the prompt carefully before coding.
What's the typical time complexity?+
O(n) in one or two passes. If you're doing something like rebuild-then-sort, it could hit O(n log n), but that's usually not necessary. Stay linear unless the problem explicitly asks for sorting.
Do I need to preserve the original array?+
Only if the prompt says so. Most of the time, mutate freely. If the problem mentions 'without modifying the original', then use a copy or build fresh. Check the example output.
What's the most common mistake on this type of problem at PayPal?+
Not reading the modification rule closely enough, then coding the wrong logic. Candidates also forget to handle empty input or single-element arrays. Walk through the example by hand first, then code.