Palindrome Permutation

 1 public class Solution {
 2     public boolean canPermutePalindrome(String s) {
 3         Map<Character, Integer> letters = new HashMap<>();
 4         for (char c : s.toCharArray()) {
 5             letters.put(c, letters.getOrDefault(c, 0) + 1);
 6         }
 7         boolean allowOdd = s.length() % 2 == 1 ? true : false;
 8         
 9         for (char c : letters.keySet()) {
10             if (letters.get(c) % 2 == 1 && !allowOdd) {
11                 return false;
12             }
13             allowOdd = letters.get(c) % 2 == 1 ? false : allowOdd;
14         }
15         return true;
16     }
17 }