2217. Find Palindrome With Fixed Length

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

A palindrome is a number that reads the same backwards and forwards. Palindromes cannot have leading zeros.

class Solution {
    long long to_long(string num, bool odd) {
        string rev = num;
        reverse(rev.begin(), rev.end());
        if(odd) num.pop_back();
        return stol(num+rev);
    }
public:
    vector<long long> kthPalindrome(vector<int>& queries, int intLength) {
        int len = (intLength + 1) / 2;
        long base = pow(10,len-1);
        vector<long long> res;
        for(auto& q : queries) {
            string num = to_string(base + q - 1);
            if(num.length() != len) {
                res.push_back(-1);
            } else {
                res.push_back(to_long(num, intLength & 1));
            }
        }
        return res;
    }
};