389. Find the Difference

/*Given two strings s and t which consist of only lowercase letters.

String t is generated by random shuffling string s and then add one more letter at a random position.

Find the letter that was added in t.

Example:

Input:
s = "abcd"
t = "abcde"

Output:
e

Explanation:
'e' is the letter that was added.*/

public class Solution {
    public char findTheDifference(String s, String t) {
        int[] ss = new int[26];
        for(int i = 0; i < s.length(); i++) {
            ss[s.charAt(i)-'a']++;
        }
        for(int i = 0; i < t.length(); i++) {
            ss[t.charAt(i)-'a']--;
        }
        for(int i = 0; i < ss.length; i++) {
            if(ss[i] != 0) {
                return (char)(i+'a');
            }
        }
        return t.charAt(0);
    }
}

//set an array stores the occurrence times of each letter with the index as 26 letters;
//tranverse the String s, add the occurrence times of each letter to the array
//tranverse the String t, minus the occurrence times of each letter to the array
//all the letters' conrespondingly value in the array are 0 except the one only occurence once.
//transe the array, find the index which value is not 0