<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> store;
    vector<string> letterCasePermutation(string s) {
        aux(s, "", store);
        return store;
    }

    void aux(string s, string newS, vector<string>& store){
        if(s.size() == 0){
            store.push_back(newS);
            return;
        }

        if(isalpha(s[0])){
            newS.push_back(s[0]);
            aux(string(s.begin()+1, s.end()), newS, store);

            newS.pop_back();

            if(isupper(s[0])){
                newS.push_back(tolower(s[0]));
                aux(string(s.begin()+1, s.end()), newS, store);
            }
            else{
            newS.push_back(toupper(s[0]));
            aux(string(s.begin()+1, s.end()), newS, store);
            }

        }
        else{
            newS.push_back(s[0]);
            aux(string(s.begin()+1, s.end()), newS, store);
        }
    }
};
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