Snapchat·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

Apr 2026Remote

Summary

Snapchat coding interview that went deep into numerical methods territory. Not what I was expecting from a social media company, but here we are.

Questions Asked (1)

Implement sin(x) from scratch without using any built-in trig functions, accurate to within a specified precision like 1e-7.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I knew Taylor series was the right direction but blanked for a solid minute on the range reduction part.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem: discuss input range, precision requirements, and performance constraints. Then propose using a Taylor series expansion with range reduction to improve accuracy and convergence. Finally, discuss trade-offs between different methods (e.g., Taylor, CORDIC, minimax polynomials) and how to handle edge cases like large inputs.

Pro tip: Mention that for production code, you'd use a minimax polynomial or lookup table for better performance, but for an interview, a Taylor series with range reduction demonstrates core algorithmic thinking. Also, always test with edge cases like x=0, very large x, and negative x.

1. Clarify requirements

Ask about the input range (e.g., radians, any real number), required precision (1e-7), and performance constraints. Confirm whether built-in functions like exponentiation or factorial are allowed.

2. Choose an algorithm

Select a method such as Taylor series, CORDIC, or minimax polynomial approximation. Explain why Taylor series is a good starting point for its simplicity and accuracy for small inputs.

3. Implement range reduction

Reduce the input angle to a small interval (e.g., [-π/4, π/4]) using periodicity and symmetry identities. This ensures the Taylor series converges quickly and accurately.

4. Compute the series and handle precision

Sum terms until the next term is below the desired precision (e.g., 1e-7). Use Horner's method or iterative multiplication to avoid factorial overflow and improve efficiency.

5. Test and discuss trade-offs

Test with edge cases (0, π/2, large angles) and compare with built-in sin. Discuss trade-offs: Taylor is simple but may be slow for high precision; minimax polynomials are faster but harder to derive.

Key Points to Mention

Range reduction using periodicity (sin(x+2π)=sin(x)) and symmetry (sin(-x)=-sin(x), sin(π-x)=sin(x)).
Taylor series expansion: sin(x) = x - x^3/3! + x^5/5! - ... and its convergence properties.
Precision control: stop when term < epsilon, and consider floating-point error accumulation.
Alternative methods: CORDIC, minimax polynomial approximation, lookup tables, and their trade-offs.
Handling edge cases: very large inputs, negative inputs, and inputs near multiples of π.
Performance considerations: number of iterations, use of Horner's method, and potential for parallelization.

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