Given a string, determine if a permutation of the string could form a palindrome.

For example,
"code"-> False,"aab"-> True,"carerac"-> True.

class Solution {
    public boolean canPermutePalindrome(String s) {
        if (s == null || s.length() == 0) return true;
        int[] hash = new int[256];

        for (char c : s.toCharArray()){
            if (!Character.isLetter(c)) continue;
            hash[c]++;
        }

        boolean hasOdd = false;
        for (int i = 0; i < 256; i++){
            if (hash[i] > 0){
                if (hash[i] % 2 == 0) continue;

                if (!hasOdd){
                    hasOdd = true;
                }
                else{
                    return false;
                }
            }
        }

        return true;
    }
}