A sentence is a string of single-space separated words where 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.

Given two sentences `s1` and `s2`, return a list of all the uncommon words. You may return the answer in any order.

Example 1:

    Input: s1 = "this apple is sweet", s2 = "this apple is sour"
    Output: ["sweet","sour"]

Example 2:

    Input: s1 = "apple apple", s2 = "banana"
    Output: ["banana"]

Constraints:

- `1 <= s1.length, s2.length <= 200`
- `s1` and `s2` consist of lowercase English letters and spaces.
- `s1` and `s2` do not have leading or trailing spaces.
- All the words in `s1` and `s2` are separated by a single space.