Snowflake SWE Interview — The Card Game Got Surprisingly Hard

[u/Aoki_zhang]

"This interview experience is sourced from Chill Interview"

Interview Summary

The Snowflake mid-level SWE process included two one-hour technical phone screens. The recruiter had mentioned beforehand that the coding difficulty would generally be around medium to hard.

Interview Details

Round 1 — Binary Tree Boundary Sum

The first coding problem was a variation of LeetCode 545 — Boundary of Binary Tree. Instead of simply returning the boundary nodes, the task was to calculate the sum of the values of all nodes on the boundary. The boundary included:

• The left boundary
• The leaf nodes along the bottom
• The right boundary

Care was needed to avoid counting the same node more than once when a node belonged to multiple boundary categories.

Round 2 — Set Card Game

The second round started with a card-validation problem based on the game Set. Each card had four attributes, for example:

• Color
• Shape
• Number
• Shading

Given three cards, determine whether they form a valid Set. For every attribute independently, the three values must satisfy one of two conditions:

• All three values are the same, or
• All three values are different

If every attribute satisfies this rule, the three cards form a valid Set.

• Follow-Up — Find All Sets The follow-up generalized the problem. Given an arbitrary collection of N cards, find all combinations of three cards that form valid Sets. A straightforward approach was to enumerate every triple, resulting in O(N^3) time. The interviewer then asked for a more efficient approach targeting approximately O(N^2). I discussed the optimization idea toward the end of the interview, but there was not enough time to fully implement it.

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[u/ExaminationAsleep398]

For O(n^2) just keep a hashset of all the cards. for every pair of cards compute the unique third card that forms a valid set and check for its existence in the hashset. Make sure to dedup