<p>Given an array <code>arr</code> of 4 digits, find the latest 24-hour time that can be made using each digit <strong>exactly once</strong>.</p>

<p>24-hour times are formatted as <code>&quot;HH:MM&quot;</code>, where <code>HH</code> is between <code>00</code> and <code>23</code>, and <code>MM</code> is between <code>00</code> and <code>59</code>. The earliest 24-hour time is <code>00:00</code>, and the latest is <code>23:59</code>.</p>

<p>Return <em>the latest 24-hour time in <code>&quot;HH:MM&quot;</code> format</em>. If no valid time can be made, return an empty string.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> arr = [1,2,3,4]
<strong>Output:</strong> &quot;23:41&quot;
<strong>Explanation:</strong> The valid 24-hour times are &quot;12:34&quot;, &quot;12:43&quot;, &quot;13:24&quot;, &quot;13:42&quot;, &quot;14:23&quot;, &quot;14:32&quot;, &quot;21:34&quot;, &quot;21:43&quot;, &quot;23:14&quot;, and &quot;23:41&quot;. Of these times, &quot;23:41&quot; is the latest.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> arr = [5,5,5,5]
<strong>Output:</strong> &quot;&quot;
<strong>Explanation:</strong> There are no valid 24-hour times as &quot;55:55&quot; is not valid.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>arr.length == 4</code></li>
	<li><code>0 &lt;= arr[i] &lt;= 9</code></li>
</ul>

class Solution {
public:

    vector<vector<int>> arr;

    void getPermutations(vector<int> &temp, int idx) {
        if(idx>=4) {
            arr.push_back(temp);
            return;
        }
        for(int i=idx;i<4;++i) {
            swap(temp[i], temp[idx]);
            getPermutations(temp, idx+1);
            swap(temp[i], temp[idx]);
        }
    }

    string largestTimeFromDigits(vector<int>& digits) {
        vector<int> temp={0,1,2,3};
        getPermutations(temp, 0);
        string ans="";
        int maxVal=-1;
        for(auto v: arr) {
            string x="";
            for(auto y: v) {
                x+=to_string(digits[y]);
            }
            int val=stoi(x);
            string k=x;
            if(val>=0 && val<=2359 && val>maxVal && stoi(k.substr(0,2))<=23 && stoi(k.substr(2,2))<=59) {
                ans=k.substr(0,2)+":"+k.substr(2,2);
                maxVal=val;
            }
        }
        return ans;
    }
};
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