content: import java.util.HashMap;
  import java.util.Map;
  
  public class FindTheDifference {
      public char findTheDifference(String s, String t) {
          Map<Character, Integer> frequenciesOrigin = getFrequencies(s);
          Map<Character, Integer> frequenciesNew = getFrequencies(t);
          return difference(frequenciesOrigin, frequenciesNew);
      }
  
      private Map<Character, Integer> getFrequencies(String string) {
          Map<Character, Integer> frequencies = new HashMap<>();
          for (int index = 0 ; index < string.length() ; index++) {
              char character = string.charAt(index);
              frequencies.put(character, frequencies.getOrDefault(character, 0) + 1);
          }
          return frequencies;
      }
  
      private char difference(Map<Character, Integer> frequencies2, Map<Character, Integer> frequencies1) {
          for (Character character : frequencies1.keySet()) {
              if (frequencies1.get(character) != frequencies2.getOrDefault(character, 0)) {
                  return character;
              }
          }
          return '\0';
      }
  }
  