Frequency Interview Questions

Score a password by adding up the number of distinct characters in every one of its substrings. This Amazon question invites the quadratic enumeration and then rewards the counting insight: each character contributes to a computable number of substrings, which turns the whole total into one pass using last-seen positions. You will derive that per-character contribution, keep the running total correct, and handle a password with no repeats. Subscribers can read the full problem and the derivation.

This Amazon coding challenge requires you to analyze text sequences to identify specific segments based on frequency and length criteria. You must efficiently count portions of a string where a single character appears with a precise proportional frequency relative to an even-sized boundary. The task evaluates your string processing skills and algorithmic optimization to avoid brute-force scanning. The full problem and model solution require a subscription.

Master a classic concurrency and data structure problem featured in LinkedIn interviews, requiring the implementation of a frequency-based eviction cache with strict performance guarantees. This exercise tests your ability to combine multiple underlying data structures, such as hash maps and doubly linked lists, to achieve constant time complexity for retrieval and insertion operations. Perfecting this challenge will greatly enhance your understanding of amortized analysis and cache eviction policies. Access the complete problem explanation and verified code solution by upgrading to a paid subscription.

Learn which word most often follows each word in a training corpus, then answer lookups for any query word. This Bloomberg question is a bigram counting exercise with a precise contract: unseen words return nothing, and ties resolve alphabetically rather than arbitrarily. You will build nested counts in one pass over the sentences, decide whether to resolve the winner at training time or at query time, and keep the tie rule deterministic. The complete problem and the reference solution are available with a subscription.

Return the earliest value in an array that appears exactly once, or a sentinel when every value repeats. This Apple warm-up needs two passes and is asked to see whether you count first and then scan, rather than testing each element against the rest. You will keep the counting pass independent of the order pass, preserve the original positions, and handle an array where nothing is unique. Subscribers get the complete problem and the reference solution.