EBay New Grad OA authoritative review: data structure Hard question Building Houses in-depth analysis

Everyone is ready to apply EBay New Grad Students, we completely understand your stress and anxiety. Facing OA from a top company like eBay, every link is crucial, and the tension of "one question determines life or death" is huge.

Just recently, our elite coaching team at ProgramHelp (formed by former senior engineers from Google and Meta and alumni from prestigious schools such as CMU and Stanford) successfully accompanied and guided a student. He successfully overcame the difficulties in the first round of OA and won the highly valuable Onsite interview ticket! Share it in detail below~

EBay New Grad OA process and analysis of high risk points

Problem 1 — Count Elements with Odd Occurrences of a Digit

Problem Description

You are given an array of non-negative integers Numbers.
Your task is to count how many elements in the array contain an Odd number of occurrences of the digit '0'.

Constraints

• 1 ≤ numbers.length ≤ 1e5
• 0 ≤ numbers[i] ≤ 1e9

Example
Numbers = numbers [4, 50, 100, 65, 2000, 700, 1, 10] → answer = 3

Total = 3

Review & What are the difficulties?

This question is essentially a simple digit count, but the real mistakes are:

• 0 Itself needs to be counted (many people have written Str(n).count("0") But single element input is missed)
• There are extreme values, e.g. 1000000000
• Emphasis on digit '0', not "all digits", don't write it as a generalized version

The most reliable way to implement it is to uniformly convert string processing.

Problem 2 — Array Reduction

Problem Description

You are given an array of non-negative integers Numbers.
Perform the following algorithm repeatedly until all elements become zero:

1. Find index I Of the Leftmost non-zero element.
   Let X = numbers[i].
2. Starting from index I To the end:
   • If Numbers[j] < x, stop this step immediately and return to Step 1
   • Else subtract X From Numbers[j]
3. Repeat until all elements become 0.

Return the final state of the array.

Constraints

• 1 ≤ numbers.length ≤ 1e5
• 0 ≤ numbers[i] ≤ 1e9

Review & What are the difficulties?

On the surface it is a simulation question, but the complexity calculation is quite "engineering thinking":

• If you just write "follow the steps to simulate violently", it will easily be O(n²) and directly time out.
• The key point is that once you encounter Numbers[j] < x, the entire subtract process must be interrupted
• After the interruption, return to Step 1, so the left end always maintains a monotonic non-decreasing trend.

In engineering, the most stable way to implement this kind of problem is simulation, but to optimize "unnecessary subtracts", the overall logic implementation must be very rigorous.

Problem 3 — Building Houses

Problem Description

You are given a list of queries representing locations on an integer line where houses are built one by one.

A house can be built at a location If at least one of its neighboring points is empty.

After each insertion, return the Length of the longest contiguous segment Of houses.

Constraints

• 1 ≤ queries.length ≤ 1e5
• -1e9 ≤ queries[i] ≤ 1e9
• All query locations are unique
• All placements are guaranteed valid

Example
Queries= [2, 1, 6, 3, 5] → output = [1, 2, 1, 3, 5]

Review & What are the difficulties?

This is a standard "dynamically maintained contiguous segment" problem. The key is:

• The position range can be up to ±1e9, arrays cannot be used
• The query order is dynamic and must use hash + merge on both sides
• Both ends may belong to different segments, and they need to be unioned into a new longer segment.
• Maintain the global maximum continuous length at each step

Common practices:

• Use map/hash to record segment left and right boundaries
• Every time you insert, look to see if there is room on the left/right
• Three situations: left connection, right connection, left and right connection → need to "merge two sections"

Slightly incorrect writing of the information update sequence will result in wrong paragraphs, wrong boundaries, and wrong lengths.

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What we provide is not cheap "ghostwriting", but high-end technical insurance and professional guidance.

• Absolute authoritative endorsement: Our team members themselves are former employees of major factories. We are well aware of the interviewer's criteria and know what kind of code can be called "Clean Code" and can successfully pass automatic duplication checking and manual review.
• Real-time assistance (VO/OA Support): During the OA process, our engineers will guide you through all questions through real-time screen sharing/voice assistance without delay. Even for hard questions, we can sort out a complete solution for you within 20 minutes, and let you respond to possible real-time monitoring or follow-up questions in a professional tone.

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