<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) {
  /*      if(s.empty()) return {};
        vector<string> permutations;
        permutations.push_back(s);
        
        for(int i = 0; i < s.length(); i++) {
            if(isalpha(s[i])) {
                int n = permutations.size();
                for(int j = 0; j < n; j++) {
                    vector<char> chs(permutations[j].begin(), permutations[j].end());
                    if(islower(chs[i])) 
                        chs[i] = toupper(chs[i]);
                    else
                        chs[i] = tolower(chs[i]);
                    permutations.push_back(string( chs.begin(), chs.end() ));
                }
            }
        }
        return permutations; */
        if(s.empty()) return {};
        vector<string> permutations;
        permutations.push_back(s);
        
        for(int i = 0; i < s.length(); i++) {
            if(isalpha(s[i])){
                int n = permutations.size();
                for(int j = 0; j < n; j++) {
                    vector<char> chs(permutations[j].begin(), permutations[j].end());
                    if(islower(chs[i]))
                        chs[i] = toupper(chs[i]);
                    else
                        chs[i] = tolower(chs[i]);
                    permutations.push_back(string(chs.begin(), chs.end()));
                }
            }
        }
        return permutations;
    }
};
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