Add hailstone algorithm (keon#434)

* Add hailstone algorithm in maths

* Add hailstone in README file

* Change type terms to int

* Add hailstone test

README.md

@@ -203,6 +203,7 @@ If you want to uninstall algorithms, it is as simple as:
     - [rsa](algorithms/maths/rsa.py)
     - [sqrt_precision_factor](algorithms/maths/sqrt_precision_factor.py)
     - [summing_digits](algorithms/maths/summing_digits.py)
+    - [hailstone](algorithms/maths/hailstone.py)
 - [matrix](algorithms/matrix)
     - [sudoku_validator](algorithms/matrix/sudoku_validator.py)
     - [bomb_enemy](algorithms/matrix/bomb_enemy.py)

algorithms/maths/hailstone.py

@@ -0,0 +1,13 @@
+def hailstone(n):
+  """Return the 'hailstone sequence' from n to 1
+     n: The starting point of the hailstone sequence
+  """
+
+  sequence = [n]
+  while n > 1:
+    if n%2 != 0:
+      n = 3*n + 1
+    else: 
+      n = int(n/2)
+    sequence.append(n)
+  return sequence

tests/test_maths.py

@@ -14,7 +14,8 @@
     pythagoras,
     is_prime,
     encrypt, decrypt,
-    combination, combination_memo
+    combination, combination_memo,
+    hailstone,
 )
 
 import unittest
@@ -288,5 +289,17 @@ def test_factorial_recur(self):
         self.assertRaises(ValueError, factorial_recur, 42, -1)
 
 
+class TestHailstone(unittest.TestCase):
+    """[summary]
+    Test for the file hailstone.py
+
+    Arguments:
+        unittest {[type]} -- [description]
+    """
+    def test_hailstone(self):
+        self.assertEqual([8, 4, 2, 1], hailstone.hailstone(8))
+        self.assertEqual([10, 5, 16, 8, 4, 2, 1], hailstone.hailstone(10))
+
+
 if __name__ == "__main__":
     unittest.main()