> For the complete documentation index, see [llms.txt](https://ugopireddy.gitbook.io/leet-code-solutions/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ugopireddy.gitbook.io/leet-code-solutions/solutions-251---300/266-palindrome-permutation.md).

# 266 Palindrome Permutation

### Problem:

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 character which occurs odd number of times?

### Solutions:

```java
public class Solution {
    public boolean canPermutePalindrome(String s) {
        HashSet<Character> app = new HashSet<Character>();
        for (int i = 0; i < s.length(); i ++) {
            char c = s.charAt(i);
            if (app.contains(c)) {
                app.remove(c);
            }    
            else {
                app.add(c);
            }
        }
        return app.size() <=1;
    }
}
```