<p>Given a string <code>n</code> representing an integer, return <em>the closest integer (not including itself), which is a palindrome</em>. If there is a tie, return <em><strong>the smaller one</strong></em>.</p>

<p>The closest is defined as the absolute difference minimized between two integers.</p>

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

<pre>
<strong>Input:</strong> n = &quot;123&quot;
<strong>Output:</strong> &quot;121&quot;
</pre>

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

<pre>
<strong>Input:</strong> n = &quot;1&quot;
<strong>Output:</strong> &quot;0&quot;
<strong>Explanation:</strong> 0 and 2 are the closest palindromes but we return the smallest which is 0.
</pre>

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

<ul>
	<li><code>1 &lt;= n.length &lt;= 18</code></li>
	<li><code>n</code> consists of only digits.</li>
	<li><code>n</code> does not have leading zeros.</li>
	<li><code>n</code> is representing an integer in the range <code>[1, 10<sup>18</sup> - 1]</code>.</li>
</ul>

class Solution {
public:
    long long generatePalindrome(long long prefix, bool isEven) {
        string s = to_string(prefix);
        string rev = s.substr(0, s.length() - !isEven);
        reverse(rev.begin(), rev.end());
        return stoll(s + rev);
    }
    string nearestPalindromic(string n) {
        if (n == "1") return "0";
        
        long long num = stoll(n);
        int length = n.size();
        long long prefix = stoll(n.substr(0, (length + 1) / 2));
        
        set<long long> candidates = {
            (long long)pow(10, length - 1) - 1,
            (long long)pow(10, length) + 1,
            generatePalindrome(prefix - 1, length % 2 == 0),
            generatePalindrome(prefix, length % 2 == 0),
            generatePalindrome(prefix + 1, length % 2 == 0)
        };
        
        candidates.erase(num);
        return to_string(*min_element(candidates.begin(), candidates.end(), 
                       [num](long long a, long long b) {
                           long long diffA = abs(a - num);
                           long long diffB = abs(b - num);
                           return diffA == diffB ? a < b : diffA < diffB;
                       }));
    }
};
9100