LeetCode 299 Bulls and Cows

You are playing the following Bulls and Cows game with your friend: You write down a number and
ask your friend to guess what the number is. Each time your friend makes a guess, you provide a hint that indicates how many digits in said guess match your secret number exactly in both digit and position (called "bulls") and how many digits match the secret
number but locate in the wrong position (called "cows"). Your friend will use successive guesses and hints to eventually derive the secret number.

For example:

Secret number:  "1807"
Friend's guess: "7810"

Hint:

1

bull
and

3

cows.
(The bull is

8

,
the cows are

0

,

1

and

7

.)

Write a function to return a hint according to the secret number and friend's guess, use

A

to
indicate the bulls and

B

to indicate the cows. In the above example, your function should
return

"1A3B"

.

Please note that both secret number and friend's guess may contain duplicate digits, for example:

Secret number:  "1123"
Friend's guess: "0111"

In this case, the 1st

1

in
friend's guess is a bull, the 2nd or 3rd

1

is
a cow, and your function should return

"1A1B"

.

You may assume that the secret number and your friend's guess only contain digits, and their lengths are always equal.

关键是理解题意：

A的意思是数字正确且位置正确的个数；

B的意思是数字正确但位置不正确的个数。

public static String getHint(String secret, String guess) {
int a = 0, b = 0;
for (int i = 0; i < guess.length(); i++) {
if (guess.charAt(i) == secret.charAt(i))
a++;
}
for (int i = 0; i < guess.length(); i++) {
if (secret.contains(guess.charAt(i) + "")) {
secret = secret.replaceFirst(guess.charAt(i) + "", "");
b++;
}
}
return a + "A" + (b - a) + "B";
}