public class Solution
extends Object
949 - Largest Time for Given Digits\.
Medium
Given an array `arr` of 4 digits, find the latest 24-hour time that can be made using each digit **exactly once**.
24-hour times are formatted as `"HH:MM"`, where `HH` is between `00` and `23`, and `MM` is between `00` and `59`. The earliest 24-hour time is `00:00`, and the latest is `23:59`.
Return _the latest 24-hour time in `"HH:MM"` format_. If no valid time can be made, return an empty string.
**Example 1:**
**Input:** arr = [1,2,3,4]
**Output:** "23:41"
**Explanation:** The valid 24-hour times are "12:34", "12:43", "13:24", "13:42", "14:23", "14:32", "21:34", "21:43", "23:14", and "23:41". Of these times, "23:41" is the latest.
**Example 2:**
**Input:** arr = [5,5,5,5]
**Output:** ""
**Explanation:** There are no valid 24-hour times as "55:55" is not valid.
**Constraints:**
* `arr.length == 4`
* `0 <= arr[i] <= 9`