<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 solve(string ip, string op, vector<string> &v)
 {
    if(ip.length()==0)
    {
        v.push_back(op);
        return;
    }
    if(isalpha(ip[0]))
    {
        string op1=op;
        string op2=op;
        op1.push_back(tolower(ip[0]));
        op2.push_back(toupper(ip[0]));
        ip.erase(ip.begin()+0);
        solve(ip, op1, v);
        solve(ip, op2, v);
    }
    else
    {
        string op1= op;
        op1.push_back(ip[0]);
        ip.erase(ip.begin()+0);
        solve(ip,op1, v);
    }
 }
    vector<string> letterCasePermutation(string s) {
        string ip=s;
        string op="";
        vector<string> v;
        solve(ip, op, v);
        return v;
    }
};
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