409. Longest Palindrome

Intuition

Source: Yao Frankie

public int longestPalindrome(String s) {
  Set<Character> set = new HashSet<>();
  int pairsCount = 0;

  for (char c : s.toCharArray()) {
    if (set.remove(c)) {
      // if character exists remove and add to pairsCount
      pairsCount++;
    } else {
      set.add(c);
    }
  }

  return (pairsCount * 2) + (set.isEmpty() ? 0 : 1);
}