<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 solve(string s, int i, string& output, vector<string>& ans){
    if(i>=s.size()){
        ans.push_back(output);
        return;
    }

    output.push_back(s[i]);
    solve(s, i+1, output, ans);
    output.pop_back();
    if(s[i]>='a' && s[i]<='z') { 
            output.push_back(toupper(s[i])); 
            solve(s, i + 1, output, ans);
            output.pop_back();
        }
       else  if(s[i]>='A' && s[i]<='Z') { 
            output.push_back(tolower(s[i])); 
            solve(s, i + 1, output, ans);
            output.pop_back();
        }
   
}
    vector<string> letterCasePermutation(string s) {
        vector<string> ans;
        string output;
        solve(s, 0, output, ans);
        return ans;
    }
};
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