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Snowflake Online Assessment 2026: Longest Consecutive Sequence, Group Anagrams & Rotate Image

Snowflake's 2026 OA features three classic coding problems: longest consecutive sequence (HashSet), group anagrams (hash map), and in place matrix rotation.

By HackTheRounds Team · 2025-08-20

Overview

Snowflake's 2026 OA is relatively straightforward compared to other companies — three well-known problems that test fundamental data structure and algorithm skills. If you've done your LeetCode practice, these should feel familiar.

Problem 1: Longest Consecutive Sequence

Difficulty: Medium | Topics: HashSet, Array

Given an unsorted array of integers, find the length of the longest consecutive elements sequence. Must run in O(n) time.

Approach: Add all numbers to a HashSet. For each number, check if num - 1 exists in the set — if not, it's the start of a sequence. Then count upward ( num + 1 , num + 2 , ...) while elements exist in the set.

Key Insight: Only start counting from sequence beginnings (where num - 1 is absent). This ensures O(n) overall despite the inner loop.

Problem 2: Group Anagrams

Difficulty: Medium | Topics: Hash Map, String, Sorting

Given an array of strings, group all anagrams together. Return groups in any order.

Approach: Use a hash map where the key is the sorted version of each string. All anagrams produce the same sorted key. Alternatively, use a character frequency count as the key (faster than sorting).

Key Insight: The sorted-string approach is simpler to implement. The frequency-count approach is faster for long strings.

Problem 3: Rotate Image

Difficulty: Medium | Topics: Matrix, In-Place

Rotate an n×n matrix 90 degrees clockwise, in-place (no extra O(n²) space).

Approach: Two-step process: (1) transpose the matrix (swap matrix[i][j] with matrix[j][i] ), then (2) reverse each row. Together these produce a 90-degree clockwise rotation.

Key Insight: Don't try to rotate cells directly — the transpose-then-reverse approach is much cleaner and less error-prone.

Snowflake OA Prep Tips

  1. Classic LeetCode problems — Snowflake draws from well-known problems. Review the top 100 most-asked questions
  2. HashSet and HashMap patterns — at least 2 of 3 problems typically involve hashing
  3. In-place operations — they test whether you can modify data without extra space
  4. Clean code matters — Snowflake is known for high engineering standards

Explore Snowflake interview questions on HackTheRounds.