Pattern Recognition — Keywords to Technique

Triage a problem statement into a pattern bucket, then read the linked pattern note for recipes and templates.

Index: Patterns README

Mermaid flowchart (keyword triage)

Use camelCase node IDs with no spaces. Follow arrows from your best keyword match.

Pattern → doc link

Related patterns not shown as graph terminals: Merge intervals, Cyclic sort, Linked list reversal, Tree DFS.

Text decision tree (backup)

1. Input sorted / orderable to sorted

   • Pair / triplet / merge walks → Two Pointers (01).
   • “Smallest X such that …” / boundary on predicate → Binary Search (04).

2. Contiguous substring/subarray with a constraint (longest/shortest/fixed)
   → Sliding Window (02).

3. Linked list: cycle, middle, k-from-end
   → Fast & Slow (03); reversal variants → 10.

4. Graph / tree

   • Unweighted shortest path / levels → BFS (05).
   • All arrangements / paths / “try combinations” → DFS / backtracking (06).
   • Tree DP / paths → Tree DFS (11).

5. Top-k, streaming median, Dijkstra frontier
   → Heap (07).

6. Prerequisites / course schedule / build order
   → Topological sort (12).

7. Dynamic connectivity / redundant connection / Kruskal-like
   → Union-Find (13).

8. Prefix search / dictionary / autocomplete on strings
   → Trie (14).

9. “Next greater / smaller element”, histogram, temperature stack
   → Monotonic stack (15).

10. Static range sums / difference-array style updates
    → Prefix sum / difference (16).

11. XOR uniqueness, subset enumeration with bitmask
    → Bit manipulation (17).

12. Overlapping subproblems + optimal substructure
    → often DP (18); Greedy (19) when exchange argument holds; Divide & conquer (20) when subproblems are independent halves.

Cheatsheet peers: Big-O complexity, Data structure operations.