Merge pull request #14 from sjakobi/palindrome-products

New exercise: python palindrome-products

EXERCISES.txt

@@ -18,6 +18,7 @@ sum-of-multiples
 space-age
 grains
 gigasecond
+palindrome-products
 triangle
 scrabble-score
 sieve

palindrome-products/example.py

@@ -0,0 +1,18 @@
+def largest_palindrome(max_factor, min_factor=0):
+    return max(palindromes(max_factor, min_factor), key=lambda tup: tup[0])
+
+
+def smallest_palindrome(max_factor, min_factor):
+    return min(palindromes(max_factor, min_factor), key=lambda tup: tup[0])
+
+
+def palindromes(max_factor, min_factor):
+    return ((a * b, (a, b))
+            for a in range(min_factor, max_factor + 1)
+            for b in range(min_factor, a + 1)
+            if is_palindrome(a * b))
+
+
+def is_palindrome(n):
+    s = str(n)
+    return s == s[::-1]

palindrome-products/palindrome_products_test.py

@@ -0,0 +1,50 @@
+"""
+Notes regarding the implementation of smallest_palindrome and
+largest_palindrome:
+
+Both functions must take two keyword arguments:
+    max_factor -- int
+    min_factor -- int, default 0
+
+Their return value must be a tuple (value, factors) where value is the
+palindrome itself, and factors is an iterable containing both factors of the
+palindrome in arbitrary order.
+"""
+
+try:
+    from palindrome import smallest_palindrome, largest_palindrome
+except ImportError:
+    raise SystemExit('Could not find palindrome.py. Does it exist?')
+
+import unittest
+
+
+class PalindromesTests(unittest.TestCase):
+    def test_largest_palindrome_from_single_digit_factors(self):
+        value, factors = largest_palindrome(max_factor=9)
+        self.assertEqual(9, value)
+        self.assertIn(set(factors), [{1, 9}, {3, 3}])
+
+    def test_largest_palindrome_from_double_digit_factors(self):
+        value, factors = largest_palindrome(max_factor=99, min_factor=10)
+        self.assertEqual(9009, value)
+        self.assertEqual({91, 99}, set(factors))
+
+    def test_smallest_palindrome_from_double_digit_factors(self):
+        value, factors = smallest_palindrome(max_factor=99, min_factor=10)
+        self.assertEqual(121, value)
+        self.assertEqual({11}, set(factors))
+
+    def test_largest_palindrome_from_triple_digit_factors(self):
+        value, factors = largest_palindrome(max_factor=999, min_factor=100)
+        self.assertEqual(906609, value)
+        self.assertEqual({913, 993}, set(factors))
+
+    def test_smallest_palindrome_from_triple_digit_factors(self):
+        value, factors = smallest_palindrome(max_factor=999, min_factor=100)
+        self.assertEqual(10201, value)
+        self.assertEqual({101, 101}, set(factors))
+
+
+if __name__ == '__main__':
+    unittest.main()