June 2018 Update

Task/Fibonacci-sequence/Python/fibonacci-sequence-11.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]

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

@@ -1,11 +1,10 @@
-from itertools import islice
-
 def fib():
-    yield 0
-    yield 1
-    a, b = fib(), fib()
-    next(b)
+    """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(a)+next(b)
+        yield next(lhs)+next(rhs)
 
-print(tuple(islice(fib(), 10)))
+f=fib()
+print [next(f) for _ in range(9)]

Task/Fibonacci-sequence/Python/fibonacci-sequence-13.py

@@ -0,0 +1,11 @@
+from itertools import islice
+
+def fib():
+    yield 0
+    yield 1
+    a, b = fib(), fib()
+    next(b)
+    while True:
+        yield next(a)+next(b)
+
+print(tuple(islice(fib(), 10)))