2193. Minimum Number of Moves to Make Palindrome

Description

You are given a string s consisting only of lowercase English letters.

In one move, you can select any two adjacent characters of s and swap them.

Return the minimum number of moves needed to make s a palindrome.

Note that the input will be generated such that s can always be converted to a palindrome.

 

Example 1:

Input: s = "aabb"
Output: 2
Explanation:
We can obtain two palindromes from s, "abba" and "baab". 
- We can obtain "abba" from s in 2 moves: "aabb" -> "abab" -> "abba".
- We can obtain "baab" from s in 2 moves: "aabb" -> "abab" -> "baab".
Thus, the minimum number of moves needed to make s a palindrome is 2.

Example 2:

Input: s = "letelt"
Output: 2
Explanation:
One of the palindromes we can obtain from s in 2 moves is "lettel".
One of the ways we can obtain it is "letelt" -> "letetl" -> "lettel".
Other palindromes such as "tleelt" can also be obtained in 2 moves.
It can be shown that it is not possible to obtain a palindrome in less than 2 moves.

 

Constraints:

• 1 <= s.length <= 2000
• s consists only of lowercase English letters.
• s can be converted to a palindrome using a finite number of moves.

 

Solutions

Solution: Greedy

• Time complexity: O(n²)
• Space complexity: O(n)

 

JavaScript

/**
 * @param {string} s
 * @return {number}
 */
const minMovesToMakePalindrome = function (s) {
  const chars = [...s];
  let result = 0;

  while (chars.length) {
    const len = chars.length;
    const lastChar = chars.pop();
    const index = chars.indexOf(lastChar);

    if (index === -1) {
      result += Math.floor(len / 2);
    } else {
      chars.splice(index, 1);
      result += index;
    }
  }

  return result;
};