888. Uncommon Words from Two Sentences

题目描述：

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.

Example 1:

Input: A = "this apple is sweet", B = "this apple is sour"
Output: ["sweet","sour"]

Example 2:

Input: A = "apple apple", B = "banana"
Output: ["banana"]

Note:

1. 0 <= A.length <= 200
2. 0 <= B.length <= 200
3. A and B both contain only spaces and lowercase letters.

解题思路：

使用unordered_map<string，int>记录每个单词出现的次数，次数为一的单词加入返回的vector。

代码：

class Solution {
public:
    vector<string> uncommonFromSentences(string A, string B) {
        istringstream sin1(A);
        istringstream sin2(B);
        string word;
        unordered_map<string, int> words;
        vector<string> res;
        while (sin1>>word) {
            words[word]++;
        }
        while (sin2>>word) {
            words[word]++;
        }
        for (auto iter = words.begin(); iter != words.end(); ++iter) {
            if (iter->second == 1) {
                res.push_back(iter->first);
            }
        }
        return res;
    }
};