<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:
   void helper(string s, vector<string> &res, int ind){
    if(ind==s.size()){
        res.push_back(s);
        return;
    }
    if(isalpha(s[ind])){
        s[ind]=tolower(s[ind]);
    }
    helper(s, res, ind+1);

      if(isalpha(s[ind])){
        s[ind]=toupper(s[ind]);
        helper(s, res, ind+1);
      }
   }
    vector<string> letterCasePermutation(string s) {
        vector<string> res;
        helper(s, res, 0);
        return res;
        
    }
};
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