<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 {
private:
    void solve(string &s, int index, vector<string> &ans){

        // if(s[index] >= '0' && s[index] <= '9' && index <= s.length()){
        //     index = index + 1; 
        //     cout << "aaya";
        // }
        if(index == s.length()){
            ans.push_back(s);
            return;
        }
        
        solve(s, index+1,ans);
        // output = s;
        if(isalpha(s[index])){
        if(s[index] >= 'A' && s[index] <= 'Z'){
            s[index] = s[index] - 'A' + 'a';
            //ans.push_back(s);
            solve(s, index+1, ans);
            s[index] = s[index] - 'a' + 'A';
        }
        else {
            s[index] = s[index] - 'a' + 'A';
            //ans.push_back(s);
            solve(s, index+1, ans);
            s[index] = s[index] - 'A' + 'a';
        }
        
        //output += s;
        
        }
        
    }

   
public:
    vector<string> letterCasePermutation(string s) {
        
        vector<string>ans;
        
        solve(s, 0, ans);
        return ans;


    }
};
13000