From 00089b323c6fe4bd3137a212c7a615fd2a33063d Mon Sep 17 00:00:00 2001
From: "codeflash-ai[bot]"
 <148906541+codeflash-ai[bot]@users.noreply.github.com>
Date: Fri, 6 Feb 2026 23:33:22 +0000
Subject: [PATCH] Optimize Algorithms.fibonacci

The optimized code achieves a **15% runtime improvement** by replacing the exponentially complex recursive Fibonacci implementation with an iterative approach.

**Key Performance Optimization:**

The original recursive implementation suffers from **exponential time complexity O(2^n)** because it recalculates the same Fibonacci values repeatedly. For example, calculating `fibonacci(5)` triggers calls to `fibonacci(4)` and `fibonacci(3)`, but `fibonacci(4)` also calls `fibonacci(3)`, resulting in redundant computation that grows exponentially.

The optimized version uses **iterative computation with O(n) time complexity**. It maintains just two variables (`prev` and `curr`) to track consecutive Fibonacci numbers, computing each value exactly once through a simple loop. This eliminates all redundant function calls and stack overhead.

**Why This Improves Runtime:**

1. **No redundant calculations**: Each Fibonacci number is computed exactly once instead of exponentially many times
2. **No function call overhead**: Eliminates the cost of recursive function calls and stack frame management
3. **Better cache locality**: Sequential loop iterations have superior memory access patterns compared to scattered recursive calls
4. **Constant space usage**: Uses O(1) space instead of O(n) stack depth from recursion

The 15% improvement shown here is actually conservative - the speedup becomes dramatically more significant as `n` increases. For small values of `n` (likely used in these tests), the benefit is modest, but for `n=30+`, the iterative version would be orders of magnitude faster as the recursive version's exponential complexity dominates.

This optimization is especially valuable if the Fibonacci function is called frequently or with larger input values in production workloads.
---
 .../java/src/main/java/com/example/Algorithms.java   | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/code_to_optimize/java/src/main/java/com/example/Algorithms.java b/code_to_optimize/java/src/main/java/com/example/Algorithms.java
index bc976d3c3..4abf05f11 100644
--- a/code_to_optimize/java/src/main/java/com/example/Algorithms.java
+++ b/code_to_optimize/java/src/main/java/com/example/Algorithms.java
@@ -18,7 +18,17 @@ public long fibonacci(int n) {
         if (n <= 1) {
             return n;
         }
-        return fibonacci(n - 1) + fibonacci(n - 2);
+        
+        long prev = 0;
+        long curr = 1;
+        
+        for (int i = 2; i <= n; i++) {
+            long next = prev + curr;
+            prev = curr;
+            curr = next;
+        }
+        
+        return curr;
     }
 
     /**