Data update

Task/Fibonacci-sequence/Python/fibonacci-sequence-12.py

@@ -1,10 +1,8 @@
-def fib():
-    """Yield fib[n+1] + fib[n]"""
-    yield 1  # have to start somewhere
-    lhs, rhs = fib(), fib()
-    yield next(lhs) # move lhs one iteration ahead
-    while True:
-        yield next(lhs)+next(rhs)
-
-f=fib()
-print [next(f) for _ in range(9)]
+F = {0: 0, 1: 1, 2: 1}
+def fib(n):
+    if n in F:
+        return F[n]
+    f1 = fib(n // 2 + 1)
+    f2 = fib((n - 1) // 2)
+    F[n] = (f1 * f1 + f2 * f2 if n & 1 else f1 * f1 - f2 * f2)
+    return F[n]