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Uber·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Uber phone screen for a SWE role, one main coding problem about simulating a single-elimination tennis tournament, plus a harder follow-up that reversed the whole thing. Pretty approachable as phone screens go, but the follow-up had some real teeth if you weren't careful about odd-sized brackets.

Questions Asked (2)

Q1

Given an array of player rankings (length is a power of 2), simulate a single-elimination tournament where adjacent pairs compete each round and the higher-ranked player advances. Print the list of survivors after every round.

Algorithms & Data Structures
Author's notes

Straightforward simulation once you see it.

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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints and edge cases, then propose an iterative simulation that processes the array round by round, comparing adjacent pairs and collecting winners. Discuss time and space complexity, and consider optimizations or alternative approaches like using a queue or in-place updates.

Pro tip: Mention that the tournament structure is a complete binary tree, so you can simulate rounds in O(n) total time by processing the array level by level, and highlight that the number of rounds is log2(n). This shows you understand the underlying structure and can optimize beyond a naive O(n log n) approach.

1. Clarify requirements and edge cases

Ask about input format, output format (print after each round), and handle edge cases like n=1 (no rounds) or invalid input. Confirm that higher rank means better (e.g., larger number).

2. Outline the simulation algorithm

Explain that you'll iterate while the array length > 1, and in each round, create a new array by comparing adjacent pairs and keeping the higher-ranked player. Print the new array after each round.

3. Analyze complexity and optimize

State that the naive approach takes O(n log n) time due to log n rounds each scanning n elements. Propose an O(n) approach by processing the array in-place or using a queue, and note that space can be O(n) for the output or O(1) extra if printing directly.

4. Implement and test with examples

Walk through a small example (e.g., [3,1,4,2]) to demonstrate the rounds and outputs. Write clean code with clear variable names and handle printing as specified.

5. Discuss extensions and trade-offs

Mention how to handle ties, dynamic updates, or larger inputs. Compare iterative vs recursive approaches and justify your choice based on readability and performance.

Key Points to Mention

  • Time complexity: O(n) total if optimized, O(n log n) if naive; space complexity: O(n) for output or O(1) extra.
  • The tournament forms a complete binary tree; each round halves the number of players.
  • Edge cases: n=1 (no rounds), n=0 (empty array), and ensuring n is a power of 2.
  • In-place simulation: overwrite the first half of the array with winners to save space.
  • Printing after each round: ensure output format matches expectations (e.g., space-separated).
  • Alternative approaches: using a queue to process pairs, or recursion for clarity.

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

Q2

Given n, generate a seeding arrangement of ranks 1 through n such that in a single-elimination bracket, weaker players (higher rank numbers) get eliminated in earlier rounds. Solve it for any n, not just powers of 2.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

This one bit me.

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AI HintsAI Generated

Suggested Approach

Clarify the problem: we need a seeding order for ranks 1..n such that in a standard single-elimination bracket (with byes for non-powers of 2), higher-ranked players are eliminated in earlier rounds. The key is to recursively construct the bracket by placing the strongest players as far apart as possible, ensuring that in each round, the weakest remaining players face the strongest, leading to their elimination. For non-powers of 2, distribute byes to the top seeds to maintain fairness.

Pro tip: Mention that this is essentially the 'seeding' problem used in tournaments; the standard solution is to recursively interleave the top half and bottom half of the ranks. Also, note that byes should be given to the highest seeds to avoid penalizing them.

1. Understand the bracket structure

Explain that a single-elimination bracket pairs players in each round, with winners advancing. For n not a power of 2, some players get byes in the first round. The goal is to arrange ranks so that weaker players (higher numbers) lose as early as possible.

2. Define the recursive seeding pattern

For a power of 2, the standard seeding is: top half seeds are paired with bottom half in reverse order. Recursively apply this to each half. For example, for n=8: [1,8,4,5,2,7,3,6].

3. Handle non-powers of 2 with byes

Let p be the smallest power of 2 >= n. The number of byes is p - n. Assign byes to the top seeds (1..p-n) so they automatically advance to the second round. Then seed the remaining players using the standard method for p, but replace byes with the appropriate ranks.

4. Construct the seeding order

Generate the seeding list for p using recursion, then remove the byes (which are represented as dummy ranks) and compress the list to contain only ranks 1..n in the order they appear. This yields the final seeding arrangement.

5. Verify and analyze complexity

Check that the arrangement ensures weaker players are eliminated earlier. The algorithm runs in O(n) time and O(n) space. Discuss potential trade-offs: e.g., fairness vs. simplicity, and whether byes should be distributed differently.

Key Points to Mention

  • Recursive construction: split ranks into halves and interleave them to maximize separation of strong players.
  • Bye allocation: give byes to the highest seeds to avoid unfair early elimination.
  • Standard seeding for powers of 2: e.g., for n=8, order is [1,8,4,5,2,7,3,6].
  • Handling non-powers of 2: use the next power of 2 and replace dummy ranks with byes.
  • Time and space complexity: O(n) time and O(n) space using recursion or iterative generation.
  • Edge cases: n=1 (trivial), n=2, n=3 (one bye), and large n.

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