949. Largest Time for Given Digits --------E

Q:

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:

1. A.length == 4
2. 0 <= A[i] <= 9

A:

class Solution {
public:
    string largestTimeFromDigits(vector<int>& A) {
        int ans = -1;

        // Choose different indices i, j, k, l as a permutation of 0, 1, 2, 3
        for (int i = 0; i < 4; ++i)
            for (int j = 0; j < 4; ++j) 
                if (j != i)
                    for (int k = 0; k < 4; ++k) 
                        if (k != i && k != j) {
                            int l = 6 - i - j - k;
                            // For each permutation of A[i], read out the time and
                            // record the largest legal time.
                            int hours = 10 * A[i] + A[j];
                            int mins = 10 * A[k] + A[l];
                            if (hours < 24 && mins < 60)
                                ans = max(ans, hours * 60 + mins);
                        }

        if(ans <0)
            return "";
        string h = to_string(ans/60);
        if(h.length()==1)
            h = "0"+h;
        string m = to_string(ans%60);
        if(m.length()==1)
            m = "0"+m;
        return h + ":" + m;
    }
};