coinflip.py

import random

def PlayGame():
  CoinState = [0,0]
  AllHeads = 0
  nFlips = 0
  while (AllHeads != 1):

    for i in range(0,2):
      nFlips += 1
      if (random.random() > 0.5):
        CoinState[i] = 1

    if (CoinState[1] != CoinState[0]):
      for i in range(0,2):
        while (CoinState[i] == 1):
          nFlips += 1
          if (random.random() <= 0.5):
            CoinState[i] = 0
    elif (CoinState[1] == 1):
      AllHeads = 1

  return nFlips

nTrials = 1000000
nFlips = 0
for i in range(0,nTrials):
  nFlips += PlayGame()
print nFlips*1./nTrials