<p>Given an integer array <code>queries</code> and a <strong>positive</strong> integer <code>intLength</code>, return <em>an array</em> <code>answer</code> <em>where</em> <code>answer[i]</code> <em>is either the </em><code>queries[i]<sup>th</sup></code> <em>smallest <strong>positive palindrome</strong> of length</em> <code>intLength</code> <em>or</em> <code>-1</code><em> if no such palindrome exists</em>.</p>

<p>A <strong>palindrome</strong> is a number that reads the same backwards and forwards. Palindromes cannot have leading zeros.</p>

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

<pre>
<strong>Input:</strong> queries = [1,2,3,4,5,90], intLength = 3
<strong>Output:</strong> [101,111,121,131,141,999]
<strong>Explanation:</strong>
The first few palindromes of length 3 are:
101, 111, 121, 131, 141, 151, 161, 171, 181, 191, 202, ...
The 90<sup>th</sup> palindrome of length 3 is 999.
</pre>

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

<pre>
<strong>Input:</strong> queries = [2,4,6], intLength = 4
<strong>Output:</strong> [1111,1331,1551]
<strong>Explanation:</strong>
The first six palindromes of length 4 are:
1001, 1111, 1221, 1331, 1441, and 1551.
</pre>

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

<ul>
	<li><code>1 &lt;= queries.length &lt;= 5 * 10<sup>4</sup></code></li>
	<li><code>1 &lt;= queries[i] &lt;= 10<sup>9</sup></code></li>
	<li><code>1 &lt;= intLength&nbsp;&lt;= 15</code></li>
</ul>

#include <vector>
#include <cmath>
using namespace std;

class Solution {
public:
    long long generatePalindrome(long long half, int intLength) {
        string halfStr = to_string(half);
        string fullStr = halfStr;
        
        if (intLength % 2 == 0) {
            fullStr += string(halfStr.rbegin(), halfStr.rend());
        } else {
            fullStr += string(halfStr.rbegin() + 1, halfStr.rend());
        }
        
        return stoll(fullStr);
    }

    vector<long long> kthPalindrome(vector<int>& queries, int intLength) {
        vector<long long> result;
        
        int halfLength = (intLength + 1) / 2;
        
        long long start = pow(10, halfLength - 1);
        long long end = pow(10, halfLength) - 1;
        
        for (int q : queries) {
            long long half = start + q - 1;  
            if (half > end) {
                result.push_back(-1);  
            } else {
                result.push_back(generatePalindrome(half, intLength));  
            }
        }
        
        return result;
    }
};

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