Problem

You are given a palindromic string s and an integer k.

s. If there are fewer than k distinct palindromic permutations, return an empty string.

Note: Different rearrangements that yield the same palindromic string are considered identical and are counted once.

Example 1

1
2
3
4
5

Input: s = "abba", k = 2
Output: "baab"
Explanation:
* The two distinct palindromic rearrangements of `"abba"` are `"abba"` and `"baab"`.
* Lexicographically, `"abba"` comes before `"baab"`. Since `k = 2`, the output is `"baab"`.

Example 2

1
2
3
4
5

Input: s = "aa", k = 2
Output: ""
Explanation:
* There is only one palindromic rearrangement: `"aa"`.
* The output is an empty string since `k = 2` exceeds the number of possible rearrangements.

Example 3

1
2
3
4
5

Input: s = "bacab", k = 1
Output: "abcba"
Explanation:
* The two distinct palindromic rearrangements of `"bacab"` are `"abcba"` and `"bacab"`.
* Lexicographically, `"abcba"` comes before `"bacab"`. Since `k = 1`, the output is `"abcba"`.

Constraints

  • 1 <= s.length <= 10^4
  • s consists of lowercase English letters.
  • s is guaranteed to be palindromic.
  • 1 <= k <= 10^6

Examples

Solution

Method 1 -

Code

Complexity

  • ⏰ Time complexity: O(nnnxxxnnn)
  • 🧺 Space complexity: O(nnnxxx)