1582 articles
Find Common Characters teaches frequency intersection — the element-wise minimum of character counts across multiple strings. This pattern appears in multi-set intersection problems, resource allocation, and constraint satisfaction at tech company interviews.
Jewels and Stones is the cleanest demonstration of the "build a lookup set, then query it" pattern. While the problem itself is easy, the skill it teaches — converting a repeated linear search into O(1) lookups — is fundamental to optimizing real-world code.
Find Duplicate File in System teaches content-based grouping — the foundation of file deduplication, plagiarism detection, and distributed caching. Learn to parse structured strings, extract keys, and group by those keys using a HashMap.
Group Anagrams is a medium-difficulty milestone that teaches the canonical-key grouping pattern — one of the most broadly applicable hash map techniques. Amazon, Google, and Meta use it as a filter for candidates who can design O(n k) grouping algorithms over O(n^2 k) brute-force comparisons.
Top K Frequent Elements is a classic interview problem that tests whether you know the O(n) bucket sort approach over the standard O(n log k) heap. Amazon, Google, Meta, and Microsoft all ask this problem because it reveals whether you can identify when domain constraints enable a better algorithm.