public boolean canPermutePalindrome(String s) {
    // have at most 1 single char
    Map<Character, Integer> map = new HashMap<>();
    for (int i = 0; i < s.length(); i++) {
        char c = s.charAt(i);
        if (map.containsKey(c)) {
            map.put(c, map.get(c) + 1);
        } else {
            map.put(c, 1);
        }
    }
    
    int count = 0;
    for (Integer i: map.values()) {
        if (i % 2 != 0) {
            count++;
        }
    }
    return count <= 1;
}