<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:
    def letterCasePermutation(self, s: str) -> List[str]:
        locations = []
        for i, c in enumerate(s):
            if 'a' <= c.lower() <= 'z':
                locations.append(i)
        curr = [0] * (len(locations) + 1)
        res = []
        s_list = list(s)
        while curr[0] == 0:
            temp = s_list[:]
            for capital, location in zip(curr[1:], locations):
                if capital:
                    temp[location] = temp[location].upper()
                else:
                    temp[location] = temp[location].lower()
            res.append("".join(temp))
            idx = len(curr) - 1
            while curr[idx] == 1:
                curr[idx] = 0
                idx -= 1
            curr[idx] = 1
        return res
        
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