949. Largest Time for Given Digits

Medium

30 Points

Array

String

Backtracking

Enumeration

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.

Examples

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