fibonacci

Author: ZabihollahNamazi

Sprint-2/improve_with_caches/fibonacci/fibonacci.py

@@ -1,4 +1,17 @@
 def fibonacci(n):
+    if n < 0:
+        raise ValueError("Fibonacci is not defined for negative integers.")
     if n <= 1:
         return n
-    return fibonacci(n - 1) + fibonacci(n - 2)
+        
+    # Track the last two numbers in the sequence
+    prev2 = 0  # fibonacci(0)
+    prev1 = 1  # fibonacci(1)
+    
+    # Calculate upward to n
+    for _ in range(2, n + 1):
+        current = prev1 + prev2
+        prev2 = prev1
+        prev1 = current
+        
+    return prev1