Leetcode 9/1 Largest Time for Given Digits

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: A = [1,2,3,4]
Output: "23:41"
Example 2:

Input: A = [5,5,5,5]
Output: ""
Example 3:

Input: A = [0,0,0,0]
Output: "00:00"
Example 4:

Input: A = [0,0,1,0]
Output: "10:00"
​
Constraints:

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

class Solution {
public:
    string largestTimeFromDigits(vector<int>& A) {
        sort(A.begin(),A.end());
        string ret;
        do{
            string hour={char(A[0]+'0'),char(A[1]+'0')},minute={char(A[2]+'0'),char(A[3]+'0')};
            if(hour<"24"&&minute<"60"){
                ret=hour+":"+minute;
            }
        }while(next_permutation(A.begin(),A.end()));
        return ret;
    }
};