June 2018 Update

Task/Hamming-numbers/Python/hamming-numbers-5.py

@@ -1,38 +1,13 @@
-from itertools import islice, chain, tee
+from heapq import merge
+from itertools import tee
 
-def merge(r, s):
-    # This is faster than heapq.merge.
-    rr = r.next()
-    ss = s.next()
-    while True:
-        if rr < ss:
-            yield rr
-            rr = r.next()
-        else:
-            yield ss
-            ss = s.next()
+def hamming_numbers():
+    last = 1
+    yield last
 
-def p(n):
-    def gen():
-        x = n
-        while True:
-            yield x
-            x *= n
-    return gen()
+    a,b,c = tee(hamming_numbers(), 3)
 
-def pp(n, s):
-    def gen():
-        for x in (merge(s, chain([n], (n * y for y in fb)))):
-            yield x
-    r, fb = tee(gen())
-    return r
-
-def hamming(a, b = None):
-    if not b:
-        b = a + 1
-    seq = (chain([1], pp(5, pp(3, p(2)))))
-    return list(islice(seq, a - 1, b - 1))
-
-print hamming(1, 21)
-print hamming(1691)[0]
-print hamming(1000000)[0]
+    for n in merge((2*i for i in a), (3*i for i in b), (5*i for i in c)):
+        if n != last:
+            yield n
+            last = n