<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) {
        vector<string> res;
        int n = 1 << (s.length());

        for (int i = 0; i < n; i++) {
            int temp = i;
            string str = "";
            bool is = true;
            for (int j = 0; j < s.length(); j++) {
                if (s[j] >= '0' && s[j] <= '9') {
                    if (temp&1) {
                        is = false;
                        break;
                    }
                    str.push_back(s[j]);
                } else if (temp & 1) {
                    str.push_back(toupper(s[j]));
                } else {
                    str.push_back(tolower(s[j]));
                }

                temp = temp >> 1;
            }

            if (is) {
                res.push_back(str);
            }
        }

        return res;

    }
};
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