Given an array of 4 digits, return the largest 24 hour time that can be made.
The smallest 24 hour time is 00:00, and the largest is 23:59. Starting from 00:00, a time is larger if more time has elapsed since midnight.
Return the answer as a string of length 5. If no valid time can be made, return an empty string.
Example 1:
Input: [1,2,3,4] Output: "23:41"
Example 2:
Input: [5,5,5,5] Output: ""
Note:
A.length == 40 <= A[i] <= 9