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Hudson·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Two-part coding interview for a Software Engineer role at Hudson. One simulation problem and one classic implementation task. Nothing too wild but the first problem has some tricky edge cases that can really trip you up if you're not careful about ordering.

Questions Asked (2)

Q1

There's a 1D track from position 0 to L with N players starting at various positions. A watcher stands at a fixed point and alternates looking left/right at given timestamps. Players being watched can't move. Given an end time T, how many players reach position L?

Algorithms & Data Structures
Author's notes

This one looked manageable until I actually read the event ordering rules.

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AI HintsAI Generated

Suggested Approach

Model each player's movement as a function of time, where they move right at unit speed except when the watcher's gaze is directed at them, which freezes them. Precompute the watcher's gaze direction over time and for each player determine the total frozen duration by checking if their position falls within the watched segment during each gaze interval. Then compute the final position as initial position + (T - total_frozen_time), and count how many reach or exceed L.

Pro tip: Clarify the watcher's exact behavior: does the watcher look at a single point or a segment? If a segment, specify its length. Also confirm whether players can pass each other and if multiple players can occupy the same position. These details drastically affect the solution.

1. Clarify the problem constraints

Ask about the watcher's field of view (point vs. segment), movement speed, whether players can overlap, and if they stop exactly at L or can overshoot. Confirm the input format for timestamps and positions.

2. Preprocess the watcher's schedule

Parse the alternating left/right timestamps into intervals with a direction. For each interval, determine the watched region (e.g., left of watcher or right of watcher) and the time duration.

3. Compute frozen time per player

For each player, iterate through the watcher's intervals. If the player's position at the start of an interval is within the watched region, they are frozen for that entire interval; otherwise, they move. Accumulate the total frozen time.

4. Calculate final positions and count

For each player, final position = initial position + (T - total_frozen_time). Count how many have final position >= L. Handle edge cases like players starting at L or beyond.

5. Analyze complexity and optimize

Discuss time complexity: O(N * K) where K is number of watcher intervals. Consider if K can be large and propose optimizations like sorting intervals or using binary search if needed.

Key Points to Mention

  • Modeling player movement as piecewise linear with pauses during watched intervals
  • Precomputing watcher's gaze direction and watched region for each time interval
  • Handling simultaneous events: what if a player reaches L exactly when watched?
  • Edge cases: players starting at L, watcher looking at empty region, T before first timestamp
  • Time complexity and potential optimizations for large N and many intervals
  • Clarifying assumptions about watcher's field of view and player interactions

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

Q2

Implement integer-to-decimal-string conversion for a 32-bit signed integer without using any built-in conversion functions.

Algorithms & Data Structures
Author's notes

Pretty standard but INT_MIN will break you if you just negate and go.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem constraints and edge cases, then outline a digit-by-digit extraction using division and modulo. Handle negative numbers and the INT_MIN overflow case explicitly, and test with boundary values.

Pro tip: Mention that you would use a long or unsigned type to safely handle INT_MIN, showing awareness of overflow pitfalls that trip up many candidates.

1. Clarify requirements and edge cases

Confirm that the input is a 32-bit signed integer and discuss edge cases like 0, negative numbers, and INT_MIN. Ask if the output should include a minus sign for negatives.

2. Handle sign and special cases

Check if the number is 0 and return '0'. For negative numbers, record the sign and convert to a positive value using a safe method (e.g., cast to long) to avoid overflow with INT_MIN.

3. Extract digits using division and modulo

Repeatedly take the number modulo 10 to get the least significant digit, convert it to a character, and prepend to the result. Then divide the number by 10 to move to the next digit.

4. Assemble the string and apply sign

After the loop, if the original number was negative, prepend a minus sign to the constructed string. Ensure the string is properly terminated if using C-style strings.

5. Test with boundary values

Verify the implementation with test cases: 0, positive numbers, negative numbers, INT_MAX, and INT_MIN. Walk through the logic to ensure no off-by-one errors or overflow.

Key Points to Mention

  • Handling negative numbers and the special case of INT_MIN overflow
  • Using modulo and division to extract digits in reverse order
  • Building the string efficiently (e.g., using a character array or StringBuilder)
  • Time and space complexity: O(log n) time and O(log n) space for the output
  • Avoiding built-in conversion functions like itoa or sprintf
  • Testing edge cases such as 0, INT_MAX, and INT_MIN

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