[389]找不同

package T389找不同;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class Solution {
    public static char findTheDifference(String s, String t) {
        Character result = null;
        Map<Character, Integer> sMap = new HashMap<>();
        Map<Character, Integer> tMap = new HashMap<>();
        for (Character c : s.toCharArray()) {
            if (!sMap.containsKey(c)) {
                sMap.put(c, 0);
            }
            sMap.put(c, sMap.get(c) + 1);
        }

        for (Character c : t.toCharArray()) {
            if (!tMap.containsKey(c)) {
                tMap.put(c, 0);
            }
            tMap.put(c, tMap.get(c) + 1);
        }

        Set<Map.Entry<Character, Integer>> entries = tMap.entrySet();
        for (Map.Entry<Character, Integer> entry : entries) {
            Character key = entry.getKey();
            Integer value = entry.getValue();
            if (!value.equals(sMap.get(key))) {
                result = key;
                break;
            }
        }
        return result;
    }


}

```

import collections


class Solution:
    def findTheDifference(self, s: str, t: str) -> str:
        s_m = collections.Counter(s)
        t_m = collections.Counter(t)
        for k,v in s_m.items():
            if t_m[k] == s_m[k]:
                t_m.pop(k)
            else:
                return k
        for k,_ in t_m.items():
            return k
    '''
    python 3.2之后
    collections.Counter 提供了加减方法。
    Counter(t) - Counter(s)后返回值就是多出来的字母，list()后返回即可。
    '''


    def findTheDifference2(self, s: str, t: str) -> str:
        return list(collections.Counter(t) - collections.Counter(s))[0]