Virtu Financial·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Got a coding question at Virtu Financial for a software engineer role. Pretty algorithmic, the kind of problem that looks clean on the surface but has a few edge cases that'll trip you up if you're not careful.

Questions Asked (1)

You're given two integer arrays. You can replace any contiguous subarray with a single value equal to its sum. What's the minimum total length both arrays can be reduced to while still being identical? Return -1 if it's not possible.

Algorithms & Data Structures

Author's notes

Took me a minute to even parse what 'identical' meant here since you're collapsing subarrays from both sides simultaneously.

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AI HintsAI Generated

Suggested Approach

Recognize that the operation is equivalent to partitioning each array into contiguous segments whose sums match pairwise. Use prefix sums and two pointers to greedily match segments with equal sums, counting the minimum number of segments. If total sums differ, return -1; otherwise, the answer is the number of matched segments.

Pro tip: Emphasize that the greedy two-pointer approach works because any valid partition must have matching prefix sums at segment boundaries; this also gives O(n) time after O(n) prefix sum computation, which is optimal.

1. Check total sums

Compute the sum of both arrays. If they are not equal, return -1 immediately because the total sum is invariant under the operation.

2. Compute prefix sums

Build prefix sum arrays for both input arrays to efficiently compute segment sums and compare them.

3. Greedy two-pointer matching

Use two pointers to traverse both prefix sum arrays. Whenever the current prefix sums are equal, increment the segment count and move both pointers; otherwise, advance the pointer with the smaller prefix sum.

4. Count segments

Each time the prefix sums match, it marks the end of a segment. The total number of matches is the minimum length both arrays can be reduced to.

5. Return result

After traversing both arrays completely, return the count of matched segments as the answer.

Key Points to Mention

The operation preserves the total sum of the array, so unequal sums imply impossibility.
The problem reduces to partitioning both arrays into the same number of contiguous segments with equal sums.
Prefix sums allow O(1) segment sum comparisons.
A greedy two-pointer approach finds the maximum number of matching segments, which minimizes the final length.
Time complexity is O(n) after O(n) prefix sum computation, and space complexity is O(n) for prefix sums (can be optimized to O(1) extra space).
Edge cases: empty arrays, single-element arrays, and arrays with negative numbers (prefix sums may not be monotonic, but the greedy still works because we only compare equality of prefix sums).

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