Meta·Software Engineer·Onsite - Coding / Algorithms·Intermediate

IntermediatePrefer not to say

Jun 2026

Summary

Meta SWE coding round, one algorithmic problem on minimizing round-trip flight costs. Pretty clean problem once you see the trick, but the constraint about strictly later days is the kind of thing that'll bite you if you skim the spec.

Questions Asked (1)

Given two arrays of equal length representing outbound and return flight prices indexed by day, find the minimum total cost of a valid round trip where the return day must be strictly after the departure day. Return -1 if no valid pair exists.

Algorithms & Data Structures

Author's notes

My first instinct was brute force, O(n^2) nested loops, which obviously works but dies on n=100000.

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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints and edge cases, then propose an O(n) solution using a running minimum of outbound prices. Iterate through days, maintaining the minimum outbound price seen so far, and for each day compute the total cost with the return price on that day, updating the global minimum.

Pro tip: Always discuss trade-offs between brute force and optimized solutions, and mention that you would test with edge cases like no valid pair or large inputs. This shows you consider both correctness and efficiency, which is crucial at Meta.

1. Clarify the problem

Restate the problem in your own words and ask clarifying questions about input constraints, array sizes, and whether prices can be negative or zero.

2. Discuss brute force

Mention that a naive O(n^2) solution checks all pairs (i, j) with i < j, but it's inefficient for large n.

3. Propose optimized approach

Explain that you can iterate through the days once, keeping track of the minimum outbound price seen so far, and for each day compute the total cost with the return price on that day.

4. Walk through an example

Use a small example to demonstrate how the algorithm works, showing the running minimum and the updated minimum total cost.

5. Analyze complexity and edge cases

State that the time complexity is O(n) and space is O(1). Discuss edge cases like when no valid pair exists (return -1) and arrays of length 1.

Key Points to Mention

Time and space complexity analysis
Handling edge cases (e.g., no valid pair, single-element arrays)
The importance of the return day being strictly after the departure day
Using a running minimum to avoid nested loops
Potential follow-up: what if the arrays are not equal length?
Testing the solution with examples

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