<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> letterCasePermutation(string s) {
        vector<string> ans;
        string input = s;
        string output = "";
        conv(input,output,ans,0);
        return ans;
    }

    void conv(string input, string output, vector<string> &ans, int index){
        if(input.size()==index){
            ans.push_back(output);
            return;
        }
        char a = input[index];
        if(a>=65 && a<=90){
            string output1= output+a;
            char b = a+32;
            string output2= output+b;
            conv(input,output1,ans,index+1);
            conv(input,output2,ans,index+1);
        }
        else if(a>=97 && a<=122){
            string output1= output+a;
            char b = a-32;
            string output2= output+b;
            conv(input,output1,ans,index+1);
            conv(input,output2,ans,index+1);
        }
        else{
            output+=a;
            conv(input,output,ans,index+1);
        }
    }

};
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