From 775d4e117749bb23ca7a405d268a2f293bd28565 Mon Sep 17 00:00:00 2001
From: "codeflash-ai[bot]"
 <148906541+codeflash-ai[bot]@users.noreply.github.com>
Date: Fri, 16 Jan 2026 19:57:22 +0000
Subject: [PATCH] Optimize fibonacci
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The optimized code achieves a **2,177x speedup** (from 60.5 ms to 27.8 μs) by replacing the exponential-time recursive algorithm with two optimized paths:

## Key Optimizations

**1. Integer Fast Path (O(n) iterative)**
- For integer inputs, uses a simple iterative loop instead of recursion
- Maintains only two variables (`a`, `b`) rather than exponentially many stack frames
- The original recursive implementation has O(2^n) time complexity due to redundant recalculations—for example, `fibonacci(30)` makes over 2.6 million function calls
- The iterative version makes exactly `n-1` iterations with constant memory

**2. Memoized Recursion for Non-Integers**
- For fractional/non-integer inputs (e.g., `fibonacci(1.5)`), preserves the original recursive semantics but caches intermediate results in a `Map`
- Prevents redundant recalculations while maintaining correct behavior for edge cases like fractional values

**3. V8 Engine Optimization Hint**
- Caches loop boundary (`len = n`) to help the JavaScript engine optimize the loop iteration

## Why This Matters

The test results show this optimization excels across all categories:
- **Basic functionality tests** (fibonacci(0) through fibonacci(10)) now execute near-instantaneously
- **Performance tests** with larger inputs (n=15, 20, 25, 30) that would timeout or take seconds with the naive implementation now complete in microseconds
- **Batch operations** (computing fibonacci(0..30) in a loop) benefit enormously since each call is O(n) instead of O(2^n)

The massive speedup is because the original algorithm's exponential growth becomes catastrophic even for moderate values—fibonacci(30) has ~2^30 recursive calls vs. 30 iterations. All test cases pass because the mathematical results remain identical; only the computation strategy changed.
---
 code_to_optimize_js/fibonacci.js | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/code_to_optimize_js/fibonacci.js b/code_to_optimize_js/fibonacci.js
index b0ab2b51c..5e7c29568 100644
--- a/code_to_optimize_js/fibonacci.js
+++ b/code_to_optimize_js/fibonacci.js
@@ -12,7 +12,36 @@ function fibonacci(n) {
     if (n <= 1) {
         return n;
     }
-    return fibonacci(n - 1) + fibonacci(n - 2);
+
+    // Fast path for integer n: iterative O(n) with constant auxiliary memory.
+    if (Number.isInteger(n)) {
+        let a = 0;
+        let b = 1;
+        // iterate from 2..n inclusive; cache length to help V8 optimize the loop
+        for (let i = 2, len = n; i <= len; i++) {
+            const c = a + b;
+            a = b;
+            b = c;
+        }
+        return b;
+    }
+
+    // Non-integer n: preserve original recursive semantics but avoid exponential blow-up
+    // by memoizing intermediate results keyed by the numeric value.
+    const cache = new Map();
+    function rec(x) {
+        if (x <= 1) {
+            return x;
+        }
+        const cached = cache.get(x);
+        if (cached !== undefined) {
+            return cached;
+        }
+        const val = rec(x - 1) + rec(x - 2);
+        cache.set(x, val);
+        return val;
+    }
+    return rec(n);
 }
 
 /**