class Solution {

    public char findTheDifference(String s, String t) {

        //in the middle(start) or  in the end

        //get small length

        int sn = s.length();

        int tn = t.length();

        if(sn > tn)

        return helper(s,t);

        else return helper(t,s);

    }

    char helper(String l, String s){ // larger and smaller

        int[] a = new int[26];

        int[] b = new int[26];

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

            a[l.charAt(i) - 'a'] ++;

        }

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

            b[s.charAt(i) - 'a'] ++;

        }

        for(int i = 0; i<26; i++){

            if(a[i] != b[i]) return (char)(i+'a');

        }

        return 'a';

    }

}