Pattern Template

Every file in patterns/ (except README.md) MUST follow this 9-section shape — includes ## Diagram with at least one ```mermaid block for fast visual recall.

# NN. <Pattern Name>

## TL;DR
One paragraph: what the pattern is and the kind of problem it cracks.

## Recognition Cues
- Phrases in problem statement that scream this pattern.
- Input/output shapes (sorted array, contiguous subarray, "kth", etc.).

## Diagram
One Mermaid diagram: usual control flow, pointer movement, or decision tree for when to pick this pattern. **camelCase** node IDs.

```mermaid
flowchart LR
  cueNode[Recognition cue] --> patternNode[Pattern applies]
  patternNode --> recipeNode[Run generic recipe]

Mental Model

Picture / invariant. Why it works. (e.g., "two pointers shrink the window when sum > target — sortedness gives us monotonicity.")

Generic Recipe

Numbered steps you'd code without thinking once you've matched the pattern.

1. Initialize ...
2. Loop while ...
3. Update ...
4. Return ...

Complexity

• Time: typical and worst case.
• Space: typical.

Generic Code Template

Go

func patternTemplate(input []int) int {
    // skeleton
}

JavaScript

function patternTemplate(input) {
    // skeleton
}

Variants

• Variant A — when to switch (e.g., "shrink-only" window vs "fixed-size" window).
• Variant B — common twists.

Representative Problems

At least 3 — link to real files under topics/<topic>/problems/NNN-kebab-name.md:

• Problem A (vanilla) — ../topics/<topic>/problems/NNN-kebab-name.md
• Problem B (variant) — same pattern, different constraint
• Problem C (hard) — stretch application

Anti-patterns

• When this pattern looks tempting but isn't right.
• Common bugs (off-by-one, missed shrink condition, etc.).