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Amazon·Software Engineer·Online Assessment (OA)·Intermediate

Intermediate
May 2026

Summary

Amazon SWE online assessment with a sliding window / prefix sum problem involving piecewise-constant segment coverage. Pretty clean problem but the edge cases around uncovered indices tripped me up more than I expected.

Questions Asked (1)

Q1

Given a list of segments where each segment defines a range of indices and a per-bag money value, and an integer k, find the maximum total money you can collect from any k consecutive indices. Indices not covered by any segment have value 0.

Algorithms & Data Structures
Author's notes

My first instinct was brute force, slide a window of size k across all possible positions and sum up values.

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AI HintsAI Generated

Suggested Approach

Use a difference array to efficiently mark the value at each index from all segments, then compute the prefix sum to get cumulative values. Finally, slide a window of size k over the prefix sum to find the maximum sum of any k consecutive indices.

Pro tip: Clarify edge cases upfront: what if k is larger than the array length? What if segments overlap? Handling these shows attention to detail and prevents incorrect assumptions.

1. Clarify the problem

Confirm the input format, constraints, and edge cases such as overlapping segments, k larger than the array, and negative values (if any).

2. Build the value array

Use a difference array to apply each segment's value to its range, then compute the prefix sum to get the final value at each index.

3. Compute prefix sums

Calculate the prefix sum of the value array to enable O(1) range sum queries.

4. Find maximum k-length subarray sum

Slide a window of size k over the prefix sum array, computing the sum for each window and tracking the maximum.

5. Analyze complexity

State the time and space complexity: O(n + m) time and O(n) space, where n is the number of indices and m is the number of segments.

Key Points to Mention

  • Difference array technique for efficient range updates
  • Prefix sum for O(1) range sum queries
  • Sliding window to find maximum sum of k consecutive elements
  • Handling overlapping segments by summing values
  • Time and space complexity analysis
  • Edge cases: k > n, empty segments, negative values

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.