var longestPalindrome = function(s) {
var set = new Set();
var count = 0;
for(var i=0; i<s.length; i++){
if(set.has(s[i])){
count +=2;
set.delete(s[i])
}else{
set.add(s[i])
}
}
return set.size>0 ? count+1 : count;
};