Can any one explain why can't my solution pass the OJ? I think I have the similar method compared to yours.

'''

class Solution {

public:

int longestPalindrome(string s) {

int arr[52] = {0};

int len = s.size();

for(int i = 0;i < len;++i){

if(isupper(s[i])){

++arr[s[i]-'A'];

}

else if(islower(s[i])){

++arr[(s[i]-'a')+26];

}

}

len = 0;

int max = 0;

for(int i = 0;i < 52;++i){

if(arr[i]%2 == 0){

len += arr[i];

}

else{

if(arr[i] > max){

max = arr[i];

}

}

}

return len+max;

}

};

''''

Thanks a lot!