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Task/Subtractive-generator/Python/subtractive-generator.py

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+import collections
+s= collections.deque(maxlen=55)
+#    Start with a single seed in range 0 to 10**9 - 1.
+seed = 292929
+
+#    Set s0 = seed and s1 = 1.
+#    The inclusion of s1 = 1 avoids some bad states
+#    (like all zeros, or all multiples of 10).
+s.append(seed)
+s.append(1)
+
+#    Compute s2,s3,...,s54 using the subtractive formula
+#    sn = s(n - 2) - s(n - 1)(mod 10**9).
+for n in xrange(2, 55):
+    s.append((s[n-2] - s[n-1]) % 10**9)
+
+#    Reorder these 55 values so r0 = s34, r1 = s13, r2 = s47, ...,
+#                               rn = s(34 * (n + 1)(mod 55)).
+
+r = collections.deque(maxlen=55)
+for n in xrange(55):
+    i = (34 * (n+1)) % 55
+    r.append(s[i])
+#        This is the same order as s0 = r54, s1 = r33, s2 = r12, ...,
+#                                  sn = r((34 * n) - 1(mod 55)).
+#        This rearrangement exploits how 34 and 55 are relatively prime.
+#    Compute the next 165 values r55 to r219. Store the last 55 values.
+
+
+def getnextr():
+    """get next random number"""
+    r.append((r[0]-r[31])%10**9)
+    return r[54]
+
+# rn = r(n - 55) - r(n - 24)(mod 10**9) for n >= 55
+for n in xrange(219 - 54):
+    getnextr()
+
+# now fully initilised
+# print first five numbers
+for i in xrange(5):
+    print "result = ", getnextr()