From e480520f73547a0590c36ca308f62114780c6465 Mon Sep 17 00:00:00 2001
From: "codeflash-ai[bot]"
 <148906541+codeflash-ai[bot]@users.noreply.github.com>
Date: Fri, 16 Jan 2026 22:24:54 +0000
Subject: [PATCH] Optimize fibonacci
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The optimized code achieves a **515x speedup** (from 7.21ms to 14μs) by replacing the recursive algorithm with an iterative approach that eliminates exponential redundant calculations.

**What changed:**
- **Eliminated recursion**: The original recursive implementation called `fibonacci(n-1)` and `fibonacci(n-2)` at each level, creating an exponential call tree where the same values are recalculated thousands of times (e.g., `fibonacci(2)` is computed over 10,000 times when calculating `fibonacci(20)`).
- **Iterative loop with state tracking**: The optimized version uses a simple `for` loop with two variables (`prev` and `curr`) to iteratively build up the Fibonacci sequence from bottom to top, computing each value exactly once.

**Why this is faster:**
- **Time complexity**: Reduced from O(2^n) to O(n) - for `n=30`, this means ~1 billion operations reduced to just 30 iterations.
- **Space complexity**: Reduced from O(n) call stack depth to O(1) constant memory.
- **No function call overhead**: Eliminates the overhead of thousands of recursive function calls, stack frame allocations, and returns.

**Test case performance:**
The optimization particularly benefits **larger inputs** (n≥20), where the exponential growth of the recursive approach becomes prohibitive. The test suite shows correct results for n=20, 25, and 30, which would be slow or impractical with the recursive version. Smaller inputs (n≤10) also benefit but the speedup is less pronounced since the base cases dominate.

**Impact:**
This optimization makes the function viable for production use with moderate-to-large inputs, transforming it from an academic example into a practical implementation suitable for any context where Fibonacci numbers need to be computed efficiently.
---
 code_to_optimize_js/fibonacci.js | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/code_to_optimize_js/fibonacci.js b/code_to_optimize_js/fibonacci.js
index b0ab2b51c..c4abe97a5 100644
--- a/code_to_optimize_js/fibonacci.js
+++ b/code_to_optimize_js/fibonacci.js
@@ -12,7 +12,17 @@ function fibonacci(n) {
     if (n <= 1) {
         return n;
     }
-    return fibonacci(n - 1) + fibonacci(n - 2);
+    
+    let prev = 0;
+    let curr = 1;
+    
+    for (let i = 2; i <= n; i++) {
+        const next = prev + curr;
+        prev = curr;
+        curr = next;
+    }
+    
+    return curr;
 }
 
 /**