Cows and Bulls is a code breaker game where the player has to guess a 4 digit code. In this case I have 4 letter words, this makes playing for humans much more than random guessing and some strategy is required. I have switched cows and bulls compared to wiki definition, but concept remains same.

GUI

Solver

In this tab the human is the game host, he holds the secret 4 letter word while the computer guesses. User has to provide how many cows and bulls the guess has.

Ofcourse, a computer crunching numbers is rather uninteresting, so I have a Data page to track how the program is pruning number of availabe guesses. The guesser had two algorithms, Simple and Advanced:

• Simple - The next guess is naively selected without any preprocessing. This is fast in processing each step but might take longer.

• Advanced - The next guess here is selected such that it reduces the remaining choices. Each current valid guess is evaluated and scored according to the number of choices it can eliminate. Best scoring guess if put forward to the user.

English language has around 2000 valid 4 letter words, each guess more than halves the avalanle choices. I notices the program take at max 7 tries regardless of the complexity.

Game

In this mode the system is the host and user has to guess the code. The programs provides number of cows and bulls for each guess. All previous guess and corresponding scores are printed for reference.

Code

Core of the processor is this calcuator. This takes a guess and a chosen code and generates number of cows and bulls.

def score_calc(self, guess, chosen):
	bulls = cows = 0
	for g, c in zip(guess, chosen):
		if g == c:
			cows += 1
		elif g in chosen:
			bulls += 1
	return cows, bulls

Thus any code that does not match either cows or bulls is eliminated from the dictionary of choices. Now the question is selecting the chosen code, this depends on the strategy we want to employ.

self.choices = [c for c in self.choices if self.score_calc(c, self.ans) == score]

Simple Strategy

In the simple strategy the chosen code is simply the top most item after elimination. Then repeat till a score of 4 cows is generated and voila! that is the correct guess.

if self.strategyComboBox.currentIndex() == 0 :
	return self.choices[0]

Advanced Strategy

In advanced strategy instead of selecting the top item, each item is assumed to be the chosen code and evaluated by eliminating the non matchnig codes. This is similar to simple strategy, however this is repeated for all item and the item which produces the smallest eliminated list is chosen for next guess.

if self.strategyComboBox.currentIndex() == 1 :
	max_unique = 0
	max_g = ""
	for g in self.choices:
		results_list = []
		for c in self.choices:
			(cows,bulls) = self.score_calc(g,c)
			results_list.append(str(cows) + str(bulls))
			if len(set(results_list)) < len(results_list):
				break
		if len(set(results_list)) == len(results_list):
			return  g
		elif len(set(results_list)) > max_unique:
			max_unique  = len(set(results_list))
			max_g = g
	return max_g