Hash Set

HashSet in Java

Understand how HashSet guarantees uniqueness by wrapping a HashMap internally, with average O(1) add/contains/remove.

Dictionaries and Sets

Learn how Dictionary<TKey,TValue> and HashSet<T> use hashing for near-constant-time lookups, and how to use them correctly with custom key types.

What is a Trie?

A trie, or prefix tree, is a tree-based data structure that stores strings character by character along shared paths, letting you search, insert, and check pre…

Word Ladder Problem: How Would You Solve It?

Word ladder is solved with BFS over an implicit graph where each word is a node and an edge connects two words differing by exactly one letter, because BFS exp…

Word Break Problem: How Do You Solve It?

The word break problem — deciding whether a string can be segmented into a sequence of words from a given dictionary — is solved with dynamic programming where…

The hashCode() and equals() Contract

The hashCode()/equals() contract requires that whenever two objects are equal according to equals(), they must return the identical hashCode(), so that hash-ba…