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:

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

Output:
e

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

O(n + 1) time O(26) space array solution

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public class Solution {
    public char findTheDifference(String s, String t) {
        int[] counts = new int[26];
        for (char c : s.toCharArray()) {
            counts[c - 'a']++;
        }
        for (char c : t.toCharArray()) {
            if (--counts[c - 'a'] < 0) {
                return c;
            }
        }
        return 0;
    }
}

O(n + 1) time O(1) space bit solution

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public class Solution {
    public char findTheDifference(String s, String t) {
        char res = 0;
        for (char c : s.toCharArray()) {
            res ^= c;
        }
        for (char c : t.toCharArray()) {
            res ^= c;
        }
        return res;
    }
}