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Task/Stern-Brocot-sequence/Python/stern-brocot-sequence-2.py

@@ -0,0 +1,22 @@
+>>> from itertools import takewhile, tee, islice
+>>>  from collections import deque
+>>> from fractions import gcd
+>>>
+>>> def stern_brocot():
+    sb = deque([1, 1])
+    while True:
+        sb += [sb[0] + sb[1], sb[1]]
+        yield sb.popleft()
+
+
+>>> [s for _, s in zip(range(15), stern_brocot())]
+[1, 1, 2, 1, 3, 2, 3, 1, 4, 3, 5, 2, 5, 3, 4]
+>>> [1 + sum(1 for i in takewhile(lambda x: x != occur, stern_brocot()))
+     for occur in (list(range(1, 11)) + [100])]
+[1, 3, 5, 9, 11, 33, 19, 21, 35, 39, 1179]
+>>> prev, this = tee(stern_brocot(), 2)
+>>> next(this)
+1
+>>> all(gcd(p, t) == 1 for p, t in islice(zip(prev, this), 1000))
+True
+>>>