<p>Given a string <code>s</code>, you&nbsp;can transform every letter individually to be lowercase or uppercase to create another string.</p>

<p>Return <em>a list of all possible strings we could create</em>. Return the output in <strong>any order</strong>.</p>

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

<pre>
<strong>Input:</strong> s = &quot;a1b2&quot;
<strong>Output:</strong> [&quot;a1b2&quot;,&quot;a1B2&quot;,&quot;A1b2&quot;,&quot;A1B2&quot;]
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;3z4&quot;
<strong>Output:</strong> [&quot;3z4&quot;,&quot;3Z4&quot;]
</pre>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 12</code></li>
	<li><code>s</code> consists of lowercase English letters, uppercase English letters, and digits.</li>
</ul>

class Solution {
public:
    vector<string> letterCasePermutation(string s) {
        int n = s.length();
        vector<int> indices;
        for(int i=0;i<n;i++){
            if(isalpha(s[i]))
            indices.push_back(i);
        }
        int mask = 0,m,choices = 1<<(indices.size()); //2^m choices
        vector<string> result(choices);
        while(mask<choices){
            m = mask; //0 stands for lower
            for(int i=0;i<indices.size();i++,m=m>>1){
                if(m&1){
                    if(islower(s[indices[i]]))
                        s[indices[i]] -= 32;    
                }
                else{
                    if(isupper(s[indices[i]]))
                        s[indices[i]] += 32;  
                }
            }
            result[mask] = s;
            mask++;
        }
        return result;
        
    }
};
11200