<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 backtrack(string& s, int index, string& current, vector<string>& result){
        if(index==s.size()){
             result.push_back(current);
             return ;
        }
        char c=s[index];
        if(isalpha(c)){
            current.push_back(tolower(c));
            backtrack(s, index+1, current, result);
            current.pop_back();

            current.push_back(toupper(c));
            backtrack(s, index+1, current, result);
            current.pop_back();
        }
        else{
            current.push_back(c);
            backtrack(s, index+1, current, result);
            current.pop_back();
        }


    }
    vector<string> letterCasePermutation(string s) {
        vector<string> result;
        string current="";
        backtrack(s, 0, current, result);
        return result;
    }
};
13800