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Java-based LeetCode algorithm problem solutions, regularly updated

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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.