import java.util.HashSet;

// Time Complexity : O(n)

class Solution {

public int longestPalindrome(String s) {

int length = 0;

// Create a HashSet...

HashSet<Character> set = new HashSet<>();

// Traverse every element through loop....

for(int i=0;i<s.length();i++){

// convert string to char

char ch = s.charAt(i);

// If set contains character already, remove that character & adding 2 to length...

// It means we get pair of character which is used in palindrome...

if(set.contains(ch)){

length += 2;

set.remove(ch);

}else{

// Otherwise, add the character to the hashset...

set.add(ch);

}

}

// If the size of the set is greater than zero, move length forward...

if(set.size()>0){

length++;

}

return length; // Return the length of the longest palindrome...

}

}