Microsoft·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026

Summary

Microsoft SWE coding round, one problem the whole time. It was a binary search question dressed up in a word problem, which I didn't immediately clock, so I wasted a few minutes thinking about prefix sums before the right approach clicked.

Questions Asked (1)

You have a sorted integer array and a starting index. Find the maximum number of consecutive elements starting from that index whose sum is strictly less than a given target. Design an efficient algorithm and analyze its complexity.

Algorithms & Data Structures

Author's notes

I went straight to prefix sums and a linear scan, which works but the interviewer pushed me on whether I could do better.

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AI HintsAI Generated

Suggested Approach

Clarify that the array is sorted and we need the longest contiguous subarray starting at the given index with sum < target. Use a sliding window (two pointers) to expand the right pointer while the sum is less than target, and shrink from the left if needed, but since the start is fixed, we can simply accumulate until the sum exceeds target. Analyze time and space complexity.

Pro tip: Mention that if the array contains negative numbers, the sliding window approach fails because the sum is not monotonic; in that case, we would need a different approach like prefix sums with binary search or a more complex algorithm. This shows you consider edge cases and constraints.

1. Clarify the problem

Confirm that the array is sorted, the starting index is valid, and we need the maximum number of consecutive elements from that index with sum strictly less than target. Ask about constraints (e.g., negative numbers, large input).

2. Discuss naive approach

Mention that a brute-force approach would check all possible lengths starting from the index, computing sums incrementally, which takes O(n) time in the worst case. This sets the baseline.

3. Propose efficient algorithm

Use a sliding window (two pointers) starting at the given index. Expand the right pointer and accumulate the sum until it is >= target; the number of elements added is the answer. If negative numbers are present, discuss alternative approaches.

4. Analyze complexity

The sliding window approach runs in O(k) time where k is the number of elements considered, and O(1) extra space. In the worst case, k can be n, so O(n) time.

5. Handle edge cases

Consider cases like target <= 0, empty array, starting index out of bounds, and negative numbers. Explain how the algorithm behaves or needs modification.

Key Points to Mention

Sliding window / two-pointer technique
Time complexity O(n) and space complexity O(1)
Handling negative numbers (if present, sliding window may not work)
Edge cases: target <= 0, empty array, invalid start index
Early termination when sum exceeds target
Using prefix sums for alternative approach if needed

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