How should I practice Enumerate Valid Clock Times?

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Problem · Array

Enumerate Valid Clock Times

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Problem statement

Given exactly four decimal digits in digits, enumerate every valid 24-hour time that can be formed by using each supplied occurrence exactly once.

A valid time has format HH:MM, where 00 <= HH <= 23 and 00 <= MM <= 59. Preserve leading zeroes, remove duplicate times caused by equal digits, and return the times in chronological order.

Function

enumerateValidTimes(digits: int[]) → String[]

Examples

Example 1

digits = [1,2,3,4]return = ["12:34","12:43","13:24","13:42","14:23","14:32","21:34","21:43","23:14","23:41"]

These are exactly the valid chronological arrangements; arrangements such as 31:24 are not valid 24-hour times.

Example 2

digits = [0,0,1,2]return = ["00:12","00:21","01:02","01:20","02:01","02:10","10:02","10:20","12:00","20:01","20:10","21:00"]

The two zero occurrences are both used, and duplicate permutations produce only one copy of each time.

Example 3

digits = [5,5,5,5]return = []

No arrangement has a valid hour.

Constraints

digits.length == 4.
0 <= digits[i] <= 9.