Palindrome Permutation

public class Solution {
    public boolean canPermutePalindrome(String s) {
        Map<Character, Integer> letters = new HashMap<>();
        for (char c : s.toCharArray()) {
            letters.put(c, letters.getOrDefault(c, 0) + 1);
        }
        boolean allowOdd = s.length() % 2 == 1 ? true : false;
        
        for (char c : letters.keySet()) {
            if (letters.get(c) % 2 == 1 && !allowOdd) {
                return false;
            }
            allowOdd = letters.get(c) % 2 == 1 ? false : allowOdd;
        }
        return true;
    }
}