<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 f(string s1,vector<string>&ans,int ind){
        int n=s1.size();
        if(ind==n){
            return;
        }
        string s=s1;
        f(s,ans,ind+1);
        if(isalpha(s[ind])){
            if(toupper(s[ind])==s[ind]) s[ind]=tolower(s[ind]);
            else if(tolower(s[ind])==s[ind]) s[ind]=toupper(s[ind]);
            else if(toupper(s[ind])!=s[ind]) s[ind]=toupper(s[ind]);
            else if(tolower(s[ind])!=s[ind]) s[ind]=tolower(s[ind]);
            ans.push_back(s);
        }
        (f(s,ans,ind+1));
        return;
    }
    vector<string> letterCasePermutation(string s) {
        vector<string>ans;
        int ind=0;
        f(s,ans,ind);
        set<string>temp;
        for(auto it:ans) temp.insert(it);
        ans.clear();
        ans.push_back(s);
        for(auto it:temp) ans.push_back(it);
        return ans;
    }
};
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