Problem 041

git-svn-id: file:///srv/svn/euler@74 e5f4c3ec-3c0c-11df-b522-21efaa4426b5

e041.py

@@ -0,0 +1,31 @@
+"""What is the largest n-digit pandigital prime that exists?
+
+We shall say that an n-digit number is pandigital if it makes use of all the digits 1 to n exactly once. For example, 2143 is a 4-digit pandigital and is also prime.
+
+What is the largest n-digit pandigital prime that exists?
+"""
+
+from e007 import is_prime
+from e035 import permutations
+
+def pandigital_prime_generator(n):
+  if n not in [3, 7]:
+    raise Exception('Invalid pandigital prime length')
+  for end in [3, 7, 9]:
+    digits = range(1, n + 1)
+    if end not in digits:
+      continue
+    digits.remove(end)
+    for start in sorted(permutations(digits, len(digits)), reverse=True):
+      number = int(''.join([str(i) for i in start] + [str(end)]))
+      if is_prime(number):
+        yield number
+
+def main():
+  for len in [9, 7, 3]:
+    for n in sorted(pandigital_prime_generator(len), reverse=True):
+      print 'Pandigital Prime:', n
+      return
+
+if __name__ == '__main__':
+  main()