eBay OA CodeSignal Real Questions: Piecewise Subtraction Simulation + Case-Count Breakdown

Recently several students completed eBay Online Assessments (OA) for software engineering / data-related roles. As a long-time eBay OA tutor, here is a systematic write-up of the process, question-type distribution, and easy pitfalls. One-line summary of eBay's OA style: it does not chase fancy algorithms but demands strong fundamentals, code robustness, and business understanding—the "doesn't look hard but easily capsizes" category.

1. eBay OA Overall Process

Core: the eBay OA is not "do you know the optimal solution," but "do you look like someone who can join the team and write production code."

2. Problem 1: Array Piecewise Subtraction Simulation (Simulation + Greedy)

Given a non-negative integer array numbers, repeatedly find the leftmost non-zero element x, subtract x from consecutive elements to its right until subtraction is no longer possible, and add x to the result. Return the accumulated sum.

def piecewise_subtraction(numbers):
    total = 0
    n = len(numbers)
    while True:
        # find the leftmost non-zero element
        start = -1
        for i in range(n):
            if numbers[i] != 0:
                start = i
                break
        if start == -1:
            break                    # all zeros, done
        x = numbers[start]
        total += x
        # from start rightward, subtract x from consecutive subtractable elements
        i = start
        while i < n and numbers[i] >= x:
            numbers[i] -= x
            i += 1
    return total

Focus: patience and accuracy in simulation, strict understanding of "leftmost non-zero" and the "stop condition," and correctly handling multiple iterations and array state changes. Boundary trap: students who capsize usually do not have an algorithm problem—they miss a break condition or have imprecise loop boundaries, e.g. writing "subtract the whole segment" instead of "consecutive subtractable," or missing later rounds after an element becomes 0. eBay loves this kind of problem to see whether you fit writing production-level logic.

3. Problem 2: Upper/Lower Case Counting (String Traversal)

Given a string of uppercase and lowercase English letters, return the difference between the number of uppercase and lowercase letters.

def case_difference(s):
    upper = sum(1 for ch in s if ch.isupper())
    lower = sum(1 for ch in s if ch.islower())
    return upper - lower

Focus: basic string traversal, familiarity with character ranges / ASCII / built-ins, and whether you write a clear, readable, unambiguous implementation. Reminder: the problem is trivial, but eBay looks at whether the code is clean—isupper()/islower() is more readable than hand-written ASCII ranges, and do not flip the difference direction (upper minus lower).

4. Prep Points

FAQ

Q1: Which platform is the eBay OA on?

Depending on the role, either HackerRank or CodeSignal. Some data roles add SQL / data-processing problems. Check the invite email for the platform and get familiar with the editor.

Q2: The problems aren't hard—why is it easy to fail?

eBay favors "looks simple" simulation and string problems, but they are detail-rich with low tolerance. Most who fail miss a stop condition or leave loop boundaries unclean, not the algorithm.

Q3: Where is piecewise subtraction most easily wrong?

The "consecutive subtractable" stop condition. Stop immediately when numbers[i] >= x fails rather than subtracting the whole segment. Also, end the outer loop correctly when all are zero, or it loops forever.

Q4: Should I chase optimal complexity?

eBay values "reasonable and stable" over peak optimality. Write it correct and stable first, then optimize. We offer OA assistance / OA support: question-type prediction + timed practice + a boundary self-check list to lock in what you know.

Preparing for the eBay OA?

The eBay OA tests fundamentals and robustness, not exotic puzzles. If you want timed practice on these two problems, focused work on simulation/string problems, or real-time OA assistance / OA support, reach out—send the role's JD and we will predict the question types first, then plan a practice schedule.

Add WeChat Coding0201 now to get eBay OA questions and practice.

Contact

• WeChat: Coding0201
• Email: [email protected]
• Telegram: @OAVOProxy