Amazon·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Apr 2026

Summary

Amazon SWE coding round with a pretty gnarly array/segment problem that took most of the allotted time. Not a typical sliding window question, which threw me off at first.

Questions Asked (1)

You're given an integer k (number of consecutive bags to pick) and a 2D array where each row defines a range with a start index, end index, and a per-bag value for that range. Find the maximum total money you can get by choosing k consecutive bags. Bags not covered by any segment have value 0.

Algorithms & Data Structures

Author's notes

My first instinct was a simple sliding window but the segment structure made that messy because the array isn't laid out explicitly.

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AI HintsAI Generated

Suggested Approach

Use a difference array to compute the value of each bag in O(n + m) time, then apply a sliding window of size k to find the maximum sum of k consecutive bags. This approach efficiently handles large inputs and overlapping ranges.

Pro tip: Clarify edge cases upfront, such as when k exceeds the number of bags or when ranges are out of bounds, and mention that the difference array technique is optimal for range updates. This shows attention to detail and algorithmic maturity.

1. Understand the problem and constraints

Restate the problem to ensure clarity: we need to find the maximum sum of k consecutive bags, where bag values are determined by possibly overlapping ranges. Ask about input size and value ranges to choose the right approach.

2. Compute bag values efficiently

Use a difference array to apply all range updates in O(n + m) time, where n is the number of bags and m is the number of ranges. This avoids O(n*m) naive updates.

3. Find maximum sum of k consecutive bags

Apply a sliding window of size k over the computed bag values to find the maximum sum in O(n) time. Initialize the sum of the first k bags and slide the window, updating the sum by subtracting the outgoing bag and adding the incoming bag.

4. Handle edge cases and validate

Check if k is larger than the total number of bags (return 0 or handle appropriately). Also consider negative values (though problem implies non-negative) and ensure indices are within bounds.

Key Points to Mention

Difference array technique for efficient range updates
Sliding window for finding maximum sum of k consecutive elements
Time complexity: O(n + m) for preprocessing and O(n) for sliding window, overall O(n + m)
Space complexity: O(n) for the difference array and bag values
Handling overlapping ranges correctly by summing contributions
Edge cases: k > n, empty ranges, and large input sizes

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