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 char findTheDifference(String s, String t) {
int[] res = new int[26];
for (int i = 0; i < s.length(); i++) {
res[s.charAt(i) - 'a']++;
}
for (int i = 0; i < t.length(); i++) {
if (res[t.charAt(i) - 'a'] > 0)
res[t.charAt(i)]--;
else
return t.charAt(i);
}
return (Character) null;
}