LeetCode: Palindrome Permutation

/**
Palindrome Permutation
Given a string, determine if a permutation of the string could form a palindrome.
For example, "code" -> False, "aab" -> True, "carerac" -> True.
Hint:
Consider the palindromes of odd vs even length. What difference do you notice?
Count the frequency of each character.
If each character occurs even number of times, then it must be a palindrome. How about 4. character which occurs odd number of times?
*/

public class PalindromePermutation{
//only one characater 1 time and others even number of times
public boolean canPermutePalindrome(String s) {
        Set<Character> set=new HashSet<Character>();
        for(int i=0; i<s.length(); ++i){
            if (!set.contains(s.charAt(i)))
                set.add(s.charAt(i));
            else
                set.remove(s.charAt(i));
        }
        return set.size()==0 || set.size()==1;
    }
}