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Java-based LeetCode algorithm problem solutions, regularly updated
299\. Bulls and Cows
Medium
You are playing the **[Bulls and Cows](https://en.wikipedia.org/wiki/Bulls_and_Cows)** game with your friend.
You write down a secret number and ask your friend to guess what the number is. When your friend makes a guess, you provide a hint with the following info:
* The number of "bulls", which are digits in the guess that are in the correct position.
* The number of "cows", which are digits in the guess that are in your secret number but are located in the wrong position. Specifically, the non-bull digits in the guess that could be rearranged such that they become bulls.
Given the secret number `secret` and your friend's guess `guess`, return _the hint for your friend's guess_.
The hint should be formatted as `"xAyB"`, where `x` is the number of bulls and `y` is the number of cows. Note that both `secret` and `guess` may contain duplicate digits.
**Example 1:**
**Input:** secret = "1807", guess = "7810"
**Output:** "1A3B"
**Explanation:**
Bulls are connected with a '|' and cows are underlined:
"1807"
|
"7810"
**Example 2:**
**Input:** secret = "1123", guess = "0111"
**Output:** "1A1B"
**Explanation:**
Bulls are connected with a '|' and cows are underlined:
"1123" "1123"
| or |
"0111" "0111"
Note that only one of the two unmatched 1s is counted as a cow since the non-bull digits can only be rearranged to allow one 1 to be a bull.
**Example 3:**
**Input:** secret = "1", guess = "0"
**Output:** "0A0B"
**Example 4:**
**Input:** secret = "1", guess = "1"
**Output:** "1A0B"
**Constraints:**
* `1 <= secret.length, guess.length <= 1000`
* `secret.length == guess.length`
* `secret` and `guess` consist of digits only.