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409. Longest Palindrome 🔗

Date: Jun 04, 2024

Tags: hash-table

Description

Given a string s which consists of lowercase or uppercase letters, return the length of the longest palindrome that can be built with those letters.

Letters are case sensitive, for example, "Aa" is not considered a palindrome.

Example 1:

      Input: s = "abccccdd"
      Output: 7
      Explanation: One longest palindrome that can be built is "dccaccd", whose length is 7.
      

Example 2:

      Input: s = "a"
      Output: 1
      Explanation: The longest palindrome that can be built is "a", whose length is 1.
      

Constraints:

  • 1 <= s.length <= 2000
  • s consists of lowercase and/or uppercase English letters only.

Optimal

function longestPalindrome(s: string): number {
  const len = s.length;
  if (len === 1) return 1;
  if (len === 0) return 0;

  let result = 0;
  const hash = new Map();

  for (let i = 0; i < len; i++) {
    const char = s[i];
    const prev = hash.get(char) ?? 0;

    hash.set(char, prev + 1);

    const current = hash.get(char);
    if (current % 2 === 0) result += 2;
  }

  return result !== len ? result + 1 : result;
}

export { longestPalindrome };