Problem 035

git-svn-id: file:///srv/svn/euler@62 e5f4c3ec-3c0c-11df-b522-21efaa4426b5

e035.py

@@ -0,0 +1,42 @@
+from e007 import primes
+
+class NotCircular(Exception):
+    pass
+
+def permutations(items, n):
+    if n == 0:
+        yield []
+    else:
+        for i in xrange(len(items)):
+            for cc in permutations(items[:i] + items[i + 1:], n - 1):
+                yield [items[i]] + cc
+
+def cyclic_rotation(n):
+    if n < 10:
+        yield n
+    else:
+        s = str(n)
+        for i in xrange(len(s)):
+            yield int(s[i:] + s[:i])
+
+if __name__ == '__main__':
+    MAX = 1000000
+    circular_primes = []
+    print 'Generating primes for p < {0}...'.format(MAX)
+    prime_list = primes(0, MAX)
+    print 'Searching for circular primes...'
+    for prime in prime_list:
+        try:
+            # Ensure the prime *can* be circular
+            if prime > 9:
+                for c in [n for n in str(prime) if n not in ['1', '3', '7', '9']]:
+                    raise NotCircular()
+            # Check all permutations
+            for rotation in cyclic_rotation(prime):
+                if rotation not in prime_list:
+                    raise NotCircular()
+            circular_primes.append(prime)
+        except NotCircular:
+            pass
+        # Clear all permutations from the list?
+    print 'Circular Primes ({0}): {1}'.format(len(circular_primes), circular_primes)