<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(vector<string> &ans, string ip, string op){
        if(ip.length() == 0) {
            ans.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());
            solve(ans,ip,op1);
            solve(ans,ip,op2);
        }
        else{
            string op1 = op;
            op1.push_back(ip[0]);
            ip.erase(ip.begin());
            solve(ans,ip,op1);
        }
    }

    vector<string> letterCasePermutation(string ip) {
        string op = "";
        vector<string> ans;
        solve(ans, ip, op);
        return ans;
    }
};
15000