<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 generateStrings(string s, int idx, int size, vector<string> &result){
        if(idx == size){
            result.push_back(s);
            return;
        }

        if(isdigit(s[idx])){
            generateStrings(s,idx+1,size,result);
            return;
        }

        char ch = s[idx];
        s[idx] =  tolower(s[idx]);
        generateStrings(s,idx+1,size,result);

        s[idx] =  toupper(s[idx]);
        generateStrings(s,idx+1,size,result);
        s[idx] =  ch;

    }
    vector<string> letterCasePermutation(string s) {
        vector<string> result;
        generateStrings(s,0,s.size(),result);
        return result;
    }
};
15000