DSA topics, organized by pattern.

Array and hashing problems — the bedrock of coding interviews. Master indexing, prefix sums, and hash-map tricks.

Two-pointer problems — palindromes, sorted-array pair sums, and in-place partitioning in O(n) time and O(1) space.

Sliding-window problems — find the longest, shortest, or best contiguous subrange that satisfies a constraint.

Stack problems — parentheses matching, monotonic stacks, expression evaluation, and next-greater-element.

Binary-search problems — search a sorted array in O(log n), or apply parametric search on the answer space.

Linked-list problems — reversal, cycle detection, merge, reorder, and the runner / fast-slow pointer technique.

Tree problems — DFS and BFS traversal, BST validation, path sums, and tree construction from traversals.

Trie problems — prefix-tree implementations for word lookup, autocomplete, and prefix-based search.

Heap and priority-queue problems — top-K elements, median maintenance, and event scheduling.

Backtracking problems — combinations, permutations, subsets, word search, and constraint-satisfaction puzzles.

Graph problems — DFS, BFS, topological sort, union-find, and shortest-path traversal on grids and adjacency lists.

Dynamic programming — memoize overlapping subproblems for problems that look exponential but are polynomial.

Greedy problems — locally optimal choices that produce a globally optimal answer when the structure allows it.

Interval problems — merge, schedule, detect overlap, and the meeting-rooms / non-overlapping family.

Math problems — number theory, modular arithmetic, geometry, and pure-math reasoning at the algorithmic boundary.

Bit-manipulation problems — XOR tricks, masks, popcount, and integer encoding without arithmetic.