Optimize

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description: Benchmark, analyze, and optimize a function's execution time. Produces a before/after performance table with real numbers. Never presents a change without proving it is faster.
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Execute all four phases in order. Do not skip any phase.

## Phase 1 — Establish Baseline

1. Identify the exact code to optimize.
2. Run a micro-benchmark:
   - Write a temporary micro-benchmark script in the user's workspace.
   - The script MUST contain a warm-up phase (discard ≥10 iterations).
   - The script MUST run ≥100 iterations and output the Average and P95 execution time.
   - Run the script using the terminal.
   - Delete the temporary script after recording the results.
   - *Note: If the script fails due to missing imports or dependencies, skip it and use the bash `time` command as a fallback.*
3. Record P95 and Average. Do not proceed until the benchmark runs without error.
4. Report baseline numbers before writing any new code.

## Phase 2 — Algorithmic Analysis

1. State the current Time Complexity (Big-O) explicitly.
2. State the current Space Complexity and identify the primary allocation sites.
3. Name the bottleneck precisely:
   - "Nested loops causing O(n²) scaling"
   - "Repeated string concatenation causing N heap allocations per call"
   - "Full table scan caused by missing index on `user_id`"

## Phase 3 — Refactoring

1. Rewrite using a more efficient algorithm or data structure (apply in priority order):
   - Replace Array/List lookups with Hash Sets/Dictionaries: O(N) → O(1)
   - Vectorization or batching instead of per-item iteration
   - Caching/memoization of expensive pure computations
   - Zero-allocation patterns and buffer reuse to reduce GC pressure
   - Bitwise operations where mathematically equivalent
2. Run the benchmark on the new code.
3. If the new code is not measurably faster: discard it, select a different approach, repeat.

## Phase 4 — Report

Present a Performance Report table:

| Metric | Baseline | Optimized | Δ |
|---|---|---|---|
| Average | Xms | Yms | -Z% |
| P95 | Xms | Yms | -Z% |

Follow with a one-paragraph explanation grounded in CPU/memory theory.