题目要求

We are given two sentences A and B.  (A sentence is a string of space separated words.  Each word consists only of lowercase letters.)

A word is uncommon if it appears exactly once in one of the sentences, and does not appear in the other sentence.

Return a list of all uncommon words. 

You may return the list in any order.

题目分析及思路

给定两个句子，每个句子是一个由空格隔开的词组成的字符串，每个词只含小写字母。一个词是uncommon的条件是它仅在一个句子中出现一次。最后返回所有的uncommon的词。可以建一个dict，将词作为key，出现的次数为value。最后uncommon的词即为value为1的词。

python代码

class Solution:

    def uncommonFromSentences(self, A: 'str', B: 'str') -> 'List[str]':

        a = A.split()

        b = B.split()

        c = {}

        a.extend(b)

        for e in a:

            if e not in c:

                c[e] = 1

            else:

                c[e] += 1

        return [key for key, value in c.items() if value == 1]