a demo of http://en.wikipedia.org/wiki/Bulls_and_cows

guess_number.html

//<script type="text/javascript">

var guess = (function() {
  var code = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
	var randomize = function(a, b) {
		return Math.random() < 0.5 ? -1 : 1;
	};
	var total = 10;
	var remain;
	return {
		reset: function() {
			// generate code;
			this.code = [].concat(code);
			this.code.sort(randomize);
			this.code.length = 4;
			console.log(this.code);

			// reset flags;
			remain = total;
		},
		play: function() {
			var right = false;
			var ans;
			while (remain) {
				while (!(ans = prompt("Guess it! remain:" + remain)));
				ans = ans.split("");
				document.writeln("<p>" + ans.join(",") + "</p>");
				var varify = [].concat(this.code);
				var standby = [];
				this.a = 0;
				this.b = 0;
				for (var i = 0; i < 4; i++) {
					if (ans[i] == varify[i]) {
						this.a++;
						varify[i] = -1;
					} else {
						standby.push(ans[i]);
					}
				}
				for (var i = 0; i < standby.length; i++) {
					if (varify.indexOf(parseInt(standby[i])) != -1)
						this.b++;
				}
				if (this.a == 4) {
					right = true;
					break;
				}
				document.writeln("<p>a:" + this.a + " b:" + this.b + "</p>");
				remain--;
			}
			if (right) {
				switch (remain) {
					default: alert("You win!");
				}
			} else {
				alert("You lose! code is " + this.code.join(","));

			}
		}
	}
})();

guess.reset();
guess.play();

//</script>