<p>You are given a license key represented as a string <code>s</code> that consists of only alphanumeric characters and dashes. The string is separated into <code>n + 1</code> groups by <code>n</code> dashes. You are also given an integer <code>k</code>.</p>

<p>We want to reformat the string <code>s</code> such that each group contains exactly <code>k</code> characters, except for the first group, which could be shorter than <code>k</code> but still must contain at least one character. Furthermore, there must be a dash inserted between two groups, and you should convert all lowercase letters to uppercase.</p>

<p>Return <em>the reformatted license key</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;5F3Z-2e-9-w&quot;, k = 4
<strong>Output:</strong> &quot;5F3Z-2E9W&quot;
<strong>Explanation:</strong> The string s has been split into two parts, each part has 4 characters.
Note that the two extra dashes are not needed and can be removed.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;2-5g-3-J&quot;, k = 2
<strong>Output:</strong> &quot;2-5G-3J&quot;
<strong>Explanation:</strong> The string s has been split into three parts, each part has 2 characters except the first part as it could be shorter as mentioned above.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>5</sup></code></li>
	<li><code>s</code> consists of English letters, digits, and dashes <code>&#39;-&#39;</code>.</li>
	<li><code>1 &lt;= k &lt;= 10<sup>4</sup></code></li>
</ul>

#include <string>
using namespace std;

class Solution {
public:
    string licenseKeyFormatting(string s, int k) {
        string cleanStr;
        
        // Step 1: Remove all dashes and convert to uppercase
        for (char c : s) {
            if (c != '-') {
                cleanStr += toupper(c);  // Convert to uppercase and append
            }
        }
        
        // Step 2: Prepare result with dashes after every k characters from the end
        string result;
        int len = cleanStr.length();
        int firstGroupLen = len % k;  // Length of the first group
        
        int i = 0;
        
        // Add the first group if it has a non-zero length
        if (firstGroupLen != 0) {
            result += cleanStr.substr(i, firstGroupLen);
            i += firstGroupLen;
        }
        
        // Add dashes and the next groups of k characters
        while (i < len) {
            if (!result.empty()) {
                result += '-';  // Add a dash between groups
            }
            result += cleanStr.substr(i, k);  // Add a group of k characters
            i += k;
        }
        
        return result;
    }
};

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