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Java-based LeetCode algorithm problem solutions, regularly updated
2384\. Largest Palindromic Number
Medium
You are given a string `num` consisting of digits only.
Return _the **largest palindromic** integer (in the form of a string) that can be formed using digits taken from_ `num`. It should not contain **leading zeroes**.
**Notes:**
* You do **not** need to use all the digits of `num`, but you must use **at least** one digit.
* The digits can be reordered.
**Example 1:**
**Input:** num = "444947137"
**Output:** "7449447"
**Explanation:**
Use the digits "4449477" from "**44494****7**13**7**" to form the palindromic integer "7449447".
It can be shown that "7449447" is the largest palindromic integer that can be formed.
**Example 2:**
**Input:** num = "00009"
**Output:** "9"
**Explanation:**
It can be shown that "9" is the largest palindromic integer that can be formed.
Note that the integer returned should not contain leading zeroes.
**Constraints:**
* 1 <= num.length <= 105
* `num` consists of digits.