add hth

hth.py

@@ -0,0 +1,27 @@
+#!/usr/bin/python
+from random import choice, seed
+
+def ht():
+  """Toss a coin and return H or T."""
+  return choice(["H", "T"])
+
+def numberoftosses(pattern):
+  """Return the number of tosses until we hit the pattern."""
+  s = len(pattern) * ht()
+  while s[-len(pattern):] != pattern:
+    s += ht()
+
+  return(len(s))
+
+def avgnumberoftosses(pattern, tries = 10000):
+  """Return the average number of tosses until we hit the pattern."""
+  n = 0.0
+  for t in range(tries):
+    n += numberoftosses(pattern)
+  n /= tries
+
+  return n
+
+seed()
+for pattern in "HTH", "HTT":
+  print pattern, round(avgnumberoftosses(pattern))