0389_FInd_The_Difference.java

class Solution {
    public char findTheDifference(String s, String t) {
        Map<Character, Integer> map = new HashMap<>();
        for (char c : s.toCharArray()) {
            map.put(c, map.getOrDefault(c, 0) + 1);
        }
        for (char c : t.toCharArray()) {
            if (!map.containsKey(c) || map.get(c) == 0) {
                return c;
            }  else {
                map.put(c, map.get(c) - 1);
            }
        }
        return '\0';
    }
}