<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:
    bool vis[10];
    vector<string>ans;
    int arr[10]={1,2,4,8,1,2,4,8,16,32};
    void solve(int leds,int minutes,int hours,int start){
        if(hours>11||minutes>59)return;
        if(!leds){
            if(hours<12&&minutes<60){
                string h=to_string(hours);
                string m=to_string(minutes);
                if(minutes%10==minutes)m='0'+m;
                ans.push_back(h+':'+m);
            }
        }
        for(int i=start;i<10;i++){
            if(!vis[i]){
                vis[i]=1;
                if(i<4)solve(leds-1,minutes,hours+arr[i],i+1);
                else solve(leds-1,minutes+arr[i],hours,i+1);
                vis[i]=0;
            }
        }
    }
    vector<string> readBinaryWatch(int turnedOn) {
        solve(turnedOn,0,0,0);
        return ans;
    }
};
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