389. Find the Difference

The naive way is to sort the two strings and find the different character. The code is very straightforward.

1:  class Solution {  
2:  public:  
3:    char findTheDifference(string s, string t) {  
4:      sort(s.begin(), s.end());  
5:      sort(t.begin(), t.end());  
6:      int i = 0;  
7:      for (; i < s.size(); i++) {  
8:        if (s[i] != t[i]) break;  
9:      }  
10:      return t[i];  
11:    }  
12:  };  

However, this problem is actually equivalent to the problem of "136. Single Number".

1:  class Solution {  
2:  public:  
3:    char findTheDifference(string s, string t) {  
4:      char res = 0;  
5:      for (c : s) res ^= c;  
6:      for (c : t) res ^= c;  
7:      return res;  
8:    }  
9:  };