Add iterative Fibonacci implementation

maths/fibonacci_iterative.py

@@ -0,0 +1,29 @@
+def fibonacci_iterative(n: int) -> int:
+    """
+    Return the n-th Fibonacci number using an iterative approach.
+
+    The function returns the Fibonacci number at index n where:
+    F(0) == 0, F(1) == 1, F(2) == 1, ...
+
+    Examples:
+    >>> fibonacci_iterative(0)
+    0
+    >>> fibonacci_iterative(1)
+    1
+    >>> fibonacci_iterative(7)
+    13
+    """
+    if n < 0:
+        raise ValueError("Input must be a non-negative integer")
+
+    if n == 0:
+        return 0
+    a, b = 0, 1
+    for _ in range(1, n):
+        a, b = b, a + b
+    return b
+
+
+if __name__ == "__main__":
+    # simple demonstration
+    print(fibonacci_iterative(7))  # expected 13