<p>A binary watch has 4 LEDs on the top to represent the hours (0-11), and 6 LEDs on the bottom to represent&nbsp;the minutes (0-59). Each LED represents a zero or one, with the least significant bit on the right.</p>

<ul>
	<li>For example, the below binary watch reads <code>&quot;4:51&quot;</code>.</li>
</ul>

<p><img alt="" src="https://assets.leetcode.com/uploads/2021/04/08/binarywatch.jpg" style="width: 500px; height: 500px;" /></p>

<p>Given an integer <code>turnedOn</code> which represents the number of LEDs that are currently on (ignoring the PM), return <em>all possible times the watch could represent</em>. You may return the answer in <strong>any order</strong>.</p>

<p>The hour must not contain a leading zero.</p>

<ul>
	<li>For example, <code>&quot;01:00&quot;</code> is not valid. It should be <code>&quot;1:00&quot;</code>.</li>
</ul>

<p>The minute must&nbsp;consist of two digits and may contain a leading zero.</p>

<ul>
	<li>For example, <code>&quot;10:2&quot;</code> is not valid. It should be <code>&quot;10:02&quot;</code>.</li>
</ul>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> turnedOn = 1
<strong>Output:</strong> ["0:01","0:02","0:04","0:08","0:16","0:32","1:00","2:00","4:00","8:00"]
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> turnedOn = 9
<strong>Output:</strong> []
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>0 &lt;= turnedOn &lt;= 10</code></li>
</ul>

class Solution {
public:
    vector<string> readBinaryWatch(int turnedOn) {
        vector<string> result;
        oraRicorsiva(result, turnedOn);
        return result;
    }

    void oraRicorsiva(vector<string>& result, int turnedOn, short mask=0, char accesi=0, char start=0) {
        if(accesi > turnedOn) return;
        else if(accesi == turnedOn) {
            char h = mask >> 6;
            char m = mask & 0b111111;
            if(h >= 12 || m >= 60) return;
            string ora = to_string(h);
            ora += ":";
            if(m <= 9) ora += "0";
            ora += to_string(m);
            result.push_back(ora);
        }
        else {
            for(int i = start; i < 12; ++i) {
                if(mask & (1 << i)) continue;
                else oraRicorsiva(result, turnedOn, mask | (1 << i), accesi+1, i);
            }
        }
    }
};
9900