LeetCode Patterns Guide

Subarray and substring problems with contiguous ranges.

The problem asks about a contiguous range, substring, or subarray.

Pointer movement on arrays, strings, and linked structures.

The answer depends on comparing two positions and deciding which side should move.

Monotonicity, boundary search, and answer-space search.

You can define a predicate that changes only once across the search space.

State design, recurrence, and transition order.

You are optimizing, counting, or checking feasibility over many overlapping subproblems.

Traversal patterns for trees, graphs, and grids.

The input is a tree, graph, matrix, or implicit graph of states.

Connectivity and component merging problems.

The problem is about connectivity after repeated merge operations.

Repeatedly access the current min, max, or top-k frontier.

You repeatedly need the current smallest, largest, or earliest finishing item.

Nearest greater/smaller and boundary discovery.

The problem asks for the next greater, next smaller, or nearest boundary element.

Range sums, hash + prefix counts, and query compression.

The problem asks for many range sums or counts over ranges.

Local choices backed by exchange or boundary arguments.

A local choice seems obvious and you can argue why delaying it never helps.

Systematic search with choice, recurse, and undo.

The problem asks for all combinations, permutations, subsets, or valid constructions.

Bit tricks, state compression, and integer-level reasoning.

The problem talks about subsets, masks, parity, or binary states explicitly.