LeetCode

Q：
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:eExplanation:'e' is the letter that was added.

A：

class Solution(object):    def findTheDifference(self, s, t):        """        :type s: str        :type t: str        :rtype: str        """        sDic = {}        for ch in s:            sDic[ch] = sDic.get(ch, 0) + 1        for ch in t:            if sDic.get(ch, 0) == 0:                return ch            else:                sDic[ch] -= 1 

主要思路：
先for遍历字符串s，统计每个字母出现的次数（sDic.get(ch, 0)当字典中无该键时，自动创建并取值为0）；
之后便是遍历字符串t，若遍历到的字符并不在字典当中，也就是新添加的字母，这时给它默认为0（sDic.get(ch, 0)），则值为0时返回此字符；
若遍历的字母在字典中，则在其值上减去1，若新添加的字母与之前字符串中有重复，则会出现该字符值不断减1后到达0，还有一个该字母，这时因其值已经等于0，返回。