Intuit·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026

Summary

Coding round at Intuit for a software engineer role. One algorithmic problem with a follow-up that pushed into territory I wasn't totally prepared for.

Questions Asked (1)

You're given an array of digits representing a non-negative integer (most significant digit first, no leading zeros). Add 1 to the number and return the updated digit array.

Algorithms & Data StructuresTechnical Trade-offsSystem Design

Author's notes

The base case tripped me up less than I expected.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem constraints (e.g., array length, digit range, in-place vs. new array) and then walk through a simple example. Propose a solution that traverses from the least significant digit (end of array) to the most significant, handling carry propagation, and discuss edge cases like all 9s. Analyze time and space complexity, and mention potential optimizations or trade-offs.

Pro tip: Demonstrate foresight by discussing how you would handle very large integers that don't fit in standard data types, and mention that this approach is essentially simulating manual addition, which is scalable and avoids overflow issues.

1. Clarify requirements and constraints

Ask about input size, whether the array can be modified in-place, and if there are any constraints on memory or time. Confirm that digits are 0-9 and no leading zeros except for the number 0 itself.

2. Outline the algorithm

Explain that you will iterate from the end of the array, adding 1 and propagating carry. If a digit is less than 9, increment it and return; if it's 9, set to 0 and continue. If all digits are 9, create a new array with a leading 1 followed by zeros.

3. Walk through an example

Choose a representative example (e.g., [1,2,3] -> [1,2,4] and [9,9,9] -> [1,0,0,0]) and step through the algorithm to demonstrate correctness.

4. Analyze complexity and edge cases

State that time complexity is O(n) in the worst case (all 9s) and space complexity is O(1) if in-place, or O(n) if a new array is needed for the all-9s case. Discuss edge cases: single digit, all 9s, and no carry.

5. Discuss trade-offs and optimizations

Mention alternative approaches (e.g., converting to integer, but note overflow risks) and justify why the digit-by-digit simulation is optimal. If relevant, discuss how this scales for large arrays and potential parallelization.

Key Points to Mention

Carry propagation logic and how to handle it efficiently
In-place modification vs. creating a new array, and the trade-offs
Time and space complexity analysis (O(n) time, O(1) or O(n) space)
Edge cases: all 9s, single digit, no carry, and the number 0
Avoiding integer overflow by not converting to a numeric type
Potential follow-up: how to handle adding an arbitrary number, not just 1

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