2217. Find Palindrome With Fixed Length LeetCode Solution

Last updated: February 26, 2025

In this guide, you will get 2217. Find Palindrome With Fixed Length LeetCode Solution with the best time and space complexity. The solution to Find Palindrome With Fixed Length problem is provided in various programming languages like C++, Java, and Python. This will be helpful for you if you are preparing for placements, hackathons, interviews, or practice purposes. The solutions provided here are very easy to follow and include detailed explanations.

Problem Statement
Complexity Analysis
Find Palindrome With Fixed Length solution in C++
Find Palindrome With Fixed Length solution in Java
Find Palindrome With Fixed Length solution in Python
Additional Resources

2217. Find Palindrome With Fixed Length LeetCode Solution image

Problem Statement of 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.

Example 1:

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

Example 2:

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

Constraints:

1 <= queries.length <= 5 * 104
1 <= queries[i] <= 109
1 <= intLength <= 15

Complexity Analysis

Time Complexity: O(q)
Space Complexity: O(q)

2217. Find Palindrome With Fixed Length LeetCode Solution in C++

class Solution {
 public:
  vector<long long> kthPalindrome(vector<int>& queries, int intLength) {
    const int start = pow(10, (intLength + 1) / 2 - 1);
    const int end = pow(10, (intLength + 1) / 2);
    const int mul = pow(10, intLength / 2);
    vector<long long> ans;

    for (const int query : queries)
      if (start + query > end)
        ans.push_back(-1);
      else
        ans.push_back(getKthPalindrome(query, start, mul, intLength));

    return ans;
  }

 private:
  long getKthPalindrome(int query, int start, int mul, int intLength) {
    const long prefix = start + query - 1;
    return prefix * mul + reverse(intLength % 2 == 0 ? prefix : prefix / 10);
  }

  long reverse(int num) {
    long res = 0;
    while (num > 0) {
      res = res * 10 + num % 10;
      num /= 10;
    }
    return res;
  }
};
/* code provided by PROGIEZ */

2217. Find Palindrome With Fixed Length LeetCode Solution in Java

class Solution {
  public long[] kthPalindrome(int[] queries, int intLength) {
    final int start = (int) Math.pow(10, (intLength + 1) / 2 - 1);
    final int end = (int) Math.pow(10, (intLength + 1) / 2);
    final int mul = (int) Math.pow(10, intLength / 2);
    long[] ans = new long[queries.length];

    for (int i = 0; i < queries.length; ++i)
      if (start + queries[i] > end)
        ans[i] = -1;
      else
        ans[i] = getKthPalindrome(queries[i], start, mul, intLength);

    return ans;
  }

  private long getKthPalindrome(int q, int start, int mul, int intLength) {
    final long prefix = start + q - 1;
    return prefix * mul + reverse(intLength % 2 == 0 ? prefix : prefix / 10);
  }

  long reverse(long num) {
    long res = 0;
    while (num > 0) {
      res = res * 10 + num % 10;
      num /= 10;
    }
    return res;
  }
}
// code provided by PROGIEZ

2217. Find Palindrome With Fixed Length LeetCode Solution in Python

class Solution:
  def kthPalindrome(self, queries: list[int], intLength: int) -> list[int]:
    start = pow(10, (intLength + 1) // 2 - 1)
    end = pow(10, (intLength + 1) // 2)
    mul = pow(10, intLength // 2)

    def reverse(num: int) -> int:
      res = 0
      while num:
        res = res * 10 + num % 10
        num //= 10
      return res

    def getKthPalindrome(query: int) -> int:
      prefix = start + query - 1
      return prefix * mul + reverse(prefix
                                    if intLength % 2 == 0 else prefix // 10)

    return [-1 if start + query > end else getKthPalindrome(query)
            for query in queries]
 # code by PROGIEZ

Additional Resources

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