LinkedIn·Machine Learning Engineer·Technical Phone Screen·Intermediate

Intermediate

Jul 2026

Summary

LinkedIn ML engineer interview with a geometry/math-flavored coding problem. Pretty short content to go on but the question itself is deceptively tricky if you haven't seen triangle inequality before.

Questions Asked (1)

Given an array of integers, find three elements that can form the sides of a valid triangle.

Algorithms & Data Structures

Author's notes

I knew the triangle inequality theorem but blanked on how to apply it efficiently.

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AI HintsAI Generated

Suggested Approach

First clarify the problem: return any three elements that can form a triangle, or all such triplets? Then explain the triangle inequality and the efficient O(n log n) sorting-based approach that checks consecutive triplets. If needed, discuss the brute-force O(n^3) method and why it's suboptimal.

Pro tip: Mention that after sorting, you only need to check consecutive triplets because if a valid triangle exists, one will be found among adjacent elements. This demonstrates deep understanding and avoids unnecessary complexity.

1. Clarify requirements

Ask whether to return any valid triplet or all triplets, and whether the array can have duplicates or negative numbers. This shows attention to detail and avoids misinterpretation.

2. Explain triangle inequality

State that for sides a ≤ b ≤ c, a triangle is valid if and only if a + b > c. This is the core condition to check.

3. Present brute-force approach

Describe the naive O(n^3) solution that checks all triplets, and note its inefficiency for large arrays.

4. Introduce optimized sorting approach

Sort the array in O(n log n) and then check consecutive triplets (i, i+1, i+2) for the condition a + b > c. If found, return that triplet; otherwise, no valid triangle exists.

5. Analyze complexity and edge cases

Discuss time complexity O(n log n) and space O(1) or O(n) depending on sorting. Mention edge cases like arrays with fewer than 3 elements, all zeros, or negative numbers.

Key Points to Mention

Triangle inequality: for sorted a ≤ b ≤ c, need a + b > c.
Sorting enables checking only consecutive triplets, reducing complexity.
Time complexity: O(n log n) due to sorting, O(n^3) brute-force is inefficient.
Space complexity: O(1) extra space if sorting in-place, O(n) if not.
Edge cases: array size < 3, negative numbers, duplicates, and integer overflow.
Return any valid triplet or all triplets based on clarification.

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