# Bulls and cows/Player

``````# Build a list of all possible solutions.  The regular expression weeds
# out numbers containing zeroes or repeated digits.
var candidates = (1234..9876 -> grep {|n| !("#{n}" =~ /0 | (\d) .*? \1 /x) }.map{.digits});

# Repeatedly prompt for input until the user supplies a reasonable score.
# The regex validates the user's input and then returns two numbers.
loop {
"My guess: %s   (from %d possibilities)\n" \
-> printf(guess.join, candidates.len);

if (var m = (Sys.scanln("bulls cows: ") =~ /^\h*(\d)\h*(\d)\h*\$/)) {
var (bulls, cows) = m.cap.map{.to_i}...;
bulls+cows <= 4 && return(bulls, cows);
}

say "Please specify the number of bulls and the number of cows";
}
}

func score_correct(a, b, bulls, cows) {
var (exact, loose) = (0, 0);

for i in ^4 {
a[i] == b[i] ? ++exact
: (a[i]~~b && ++loose)
}

(bulls == exact) && (cows == loose)
}

# Pick a number, display it, get the score, and discard candidates
# that don't match the score:
loop {
var guess = candidates.pick;
candidates.grep!{|n| score_correct(n, guess, bulls, cows) }
candidates.len > 1 || break
}

# Print the secret number or the error message
say (
candidates.len == 1 ? ("Your secret number is: %d" % candidates[0].join)
)
``````

Output:

#### Output:

``````My guess: 7432   (from 3024 possibilities)
bulls cows: 0 1
My guess: 9216   (from 720 possibilities)
bulls cows: 1 1
My guess: 6813   (from 128 possibilities)
bulls cows: 0 1
My guess: 9157   (from 24 possibilities)
bulls cows: 1 3