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.

Solution1：Bit Manipulation (Xor)

Time Complexity: O(N) Space Complexity: O(1)

Solution2：Hashmap(count)

Time Complexity: O(N) Space Complexity: O(N)

Solution1 Code：

class Solution {
    public char findTheDifference(String s, String t) {
        char c = 0;
        for (int i = 0; i < s.length(); ++i) {
            c ^= s.charAt(i);
        }
        for (int i = 0; i < t.length(); ++i) {
            c ^= t.charAt(i);
        }
        return c;
    }
}

Solution2 Code：

class Solution2 {
    public char findTheDifference(String s, String t) {
        int alpha[] = new int[26];
       
        for(int i = 0; i < s.length(); i++) {
            alpha[s.charAt(i) - 'a']++;
        }
        
        for(int i = 0; i < t.length(); i++) {
            alpha[t.charAt(i) - 'a']--;
            if(alpha[t.charAt(i) - 'a'] < 0) {
                return t.charAt(i);
            }
        }

        return 0;
    }
}