LeetCode389. Find the Difference

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本文介绍了一种算法，通过比较两个字符串s和t，找到在t中新增的字符。利用Python的collections.Counter模块，文章提供了两种解决方案：一是直接使用Counter对两个字符串进行计数并相减；二是将两个字符串合并，利用Counter找出出现次数为奇数的字符。

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.

思路：比较两个字符串中新添加的字符（字符顺序可能不同）。最开始想法是利用两个字符串的Counters直接相减，返回不同：

from collections import Counter
class Solution:
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """
        dic1 = Counter(s)
        dic2 = Counter(t)
        
        return(list(dic2-dic1)[0])

又想到两个字符串除了一个字符不同，剩下全都一致，那么两个字符串加起来，只有这一个多添加的字符个数为奇数。方法有很多。

from collections import Counter
class Solution:
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """
        dic = Counter(s+t)
        for k,v in dic.items():
            if v%2 !=0 :
                return k