<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> ans;
    unordered_set<string> st;

    void helper(int idx, string &temp, string s) {
        if(st.find(temp) == st.end()) {
            ans.push_back(temp);
            st.insert(temp);
        }
        for(int i=idx; i<s.size(); i++) {
            if(isalpha(temp[i]))
                temp[i] = temp[i] ^ (1<<5);
            helper(i+1, temp, s);
            if(isalpha(temp[i]))
                temp[i] = temp[i] ^ (1<<5);
        }
    }

    vector<string> letterCasePermutation(string s) {
        string temp = s; 
        helper(0, temp, s);
        return ans;    
    }
};
16000