266. Palindrome Permutation_HashSet

Given a string s, return true if a permutation of the string could form a 

palindrome and false otherwise.

Example One: 

Input: s = "code"
Output: false


Example Two: 

Input: s = "aab"
Output: true


Example Three: 

Input: s = "carerac"
Output: true

Solutions:

class Solution {
    public boolean canPermutePalindrome(String s) {

         Set < Character > set = new HashSet < > ();
        for (int i = 0; i < s.length(); i++) {
            if (!set.add(s.charAt(i)))
                set.remove(s.charAt(i));
        }
        return set.size() <= 1;
 }
}

Hints:

Logics:

• use hashSet to excude the repeat char
• if the set didn't add the char then remove the same character
• if there is one common or no character return true
• if there is more than two characters, return false

Tips:

• if (!set.add(s.charAt(i)))

  set.remove(s.charAt(i))

• know how to use the methods